Sex Cheatsheet

A Practical Reference on Sex and Sexual Health

This page is a working reference. It covers what most adults wish they had been taught: how sexual anatomy actually works, what the research supports about practice, how to recognise and address sexual difficulties, what the evidence says about contested questions, and what doesn’t work despite popular claims. The empirical picture is clearer than cultural squeamishness usually allows it to become.

I. Anatomy: What’s Actually There

A substantial number of adults have inaccurate functional knowledge of sexual anatomy, often because their early education emphasised reproduction over function or pleasure. 

Female Anatomy

• The clitoris is much larger than commonly recognised: The visible glans clitoris (the small structure at the top of the vulva) is the external tip of an internal organ. The complete clitoris includes the glans, the body (corpus), two crura (legs) that extend several centimetres along the pubic arch, and two bulbs (vestibular bulbs) that surround the vaginal opening. Total length from glans to crura tip is typically 9–11 cm. The internal structures engorge with blood during arousal and contribute substantially to the sensations of vaginal penetration. The “vaginal orgasm vs clitoral orgasm” distinction is partly an artefact of historical thinking: essentially all female orgasms involve clitoral structure stimulation; the question is whether the stimulation is direct (external glans) or indirect (internal crura and bulbs via vaginal penetration).
• The vagina is variably sensitive: Most sensory innervation is in the outer third (closest to the vaginal opening). The deeper portions have fewer nerve endings, which is why penetrative depth typically matters less than commonly assumed and why thrusting depth is less relevant than friction patterns at the outer vagina.
• The G-spot, more accurately the anterior vaginal wall region: Located on the front (anterior) wall of the vagina, approximately 5–8 cm in. The anatomy under this area includes the urethral sponge (paraurethral glands), the urethra itself, and the internal clitoral structures. Stimulation of this region produces distinct sensations in many women and contributes to a specific type of orgasm sometimes described as “deeper” than clitoral orgasm. The G-spot anatomy is contested in academic literature, with some research denying a discrete anatomical structure and other research supporting the urethral sponge framework. Stimulation of the anterior vaginal wall produces meaningful sensation in many but not all women.
• Female ejaculation: A real phenomenon distinct from urination. The fluid involves prostatic-fluid-equivalent secretions from the paraurethral glands (Skene’s glands), often described as the female prostate. The fluid is biochemically distinct from urine, though some urinary fluid may be expelled simultaneously in some women. The capacity varies substantially across women. Some women ejaculate regularly with intense orgasm; others never do.
• The pelvic floor: A muscular sling supporting the pelvic organs. Strength and tone affect sexual sensation and function. Pelvic floor dysfunction (either weakness or hypertonicity) is a common cause of sexual difficulties in women and is treatable through pelvic floor physiotherapy. Kegel exercises are well-known but often performed incorrectly and may worsen hypertonic conditions.
• The cervix: The lower portion of the uterus that extends into the vagina. Cervical stimulation produces pleasure for some women and discomfort for others. The cervix shifts position during arousal (rising up and away from the vaginal opening), which is why deep penetration that’s uncomfortable when not fully aroused may become pleasurable when more aroused.

Male Anatomy

• The penis: The shaft contains three columns of erectile tissue: two corpora cavernosa (top) and the corpus spongiosum (bottom, surrounding the urethra). The glans (head) is the most densely innervated area. The frenulum, on the underside of the glans, is particularly sensitive in most men. The corona (the rim of the glans) is also densely innervated.
• Penis size and function: Average erect penis length is approximately 13 cm (5.1 inches), based on a 2015 meta-analysis of measured (not self-reported) lengths. Average circumference is approximately 11.7 cm (4.6 inches). The popular framing of length as the primary dimension is misleading: female partner survey research consistently identifies girth as more relevant than length for partnered sexual satisfaction, since girth produces friction at the outer vagina where most sensation is located. Length matters mainly to the extent that very short or very long can be problematic for specific positions and partners.
• The prostate: A walnut-sized gland surrounding the urethra below the bladder. The prostate produces a portion of seminal fluid and contracts during ejaculation. Prostate stimulation through the rectum (or with sufficient pressure through the perineum) produces distinct pleasure in many men and is associated with intense orgasms in some. The prostate is sometimes called the “male G-spot” and is anatomically the equivalent of the female paraurethral glands.
• The perineum: The area between the scrotum and anus. Substantial pleasure nerve density and indirect access to internal prostate stimulation. Often underused in partnered sex.
• The pelvic floor in men: The same muscular sling as in women, supporting pelvic organs and affecting sexual function. Pelvic floor strength influences erectile function, ejaculation control, and orgasm intensity. Pelvic floor exercises in men are well-supported by research for erectile difficulties and premature ejaculation.
• Testicular descent and function: Testes hang below the body to maintain a temperature approximately 2°C below core body temperature, which is required for normal spermatogenesis. Tight clothing, prolonged sitting, hot baths, and laptop heat all elevate testicular temperature and can affect sperm production.

Anatomical Knowledge as Practical Skill

Many sexual difficulties resolve when partners have accurate functional knowledge of each other’s anatomy. The clitoris is not “near” the vagina; it surrounds it. The urethral sponge is not mythical; it’s anatomically locatable. The prostate is accessible through the perineum or rectum. The cervix shifts during arousal. These are basic facts that substantially shape what works in partnered sex.

II. Sexual Response: The Underlying Architecture

The dual control model from Optimizing Pleasure provides the foundational architecture. Sexual response involves a sexual excitation system (the accelerator) and a sexual inhibition system (the brakes). Both operate in both sexes; individual variation in their relative sensitivity substantially shapes sexual experience.

Phases of Sexual Response

The Masters and Johnson linear model (excitement, plateau, orgasm, resolution) captured something about male sexual response, but inadequately represented female response. The Basson circular model better describes responsive desire patterns common in women and in long-term partnerships of both sexes: desire emerges in response to sexual context rather than spontaneously initiating it.

The integration of both models is closer to what happens:

1. Triggering stimulus: Visual, tactile, contextual, fantasy-based, or emotional. The accelerator activates.
2. Subjective arousal: Conscious awareness of sexual interest. May or may not correlate with genital arousal (especially in women, per Chivers’s research).
3. Genital arousal: Vasocongestion produces erection in men and engorgement of vulvar structures and lubrication in women. Heart rate, blood pressure, and breathing rate rise.
4. Plateau: Sustained arousal with increasing tension, particularly in the pelvic muscles. The point at which orgasm becomes likely if stimulation continues.
5. Orgasm: Rhythmic contractions of pelvic floor and genital musculature; intense pleasure; neurochemical release.
6. Resolution: Return to baseline. In men, an absolute refractory period during which another erection or orgasm isn’t possible.

Each phase can be disrupted independently. Desire can be low without dysfunction. Arousal can be impaired despite intact desire. Orgasm can be difficult or impossible despite intact arousal. Treating each phase requires recognising which phase is involved.

What Affects Each Phase

• Desire: Affected by hormones (testosterone, particularly), relationship quality, stress, fatigue, medications (particularly SSRIs and many psychiatric medications), body image, depression, and the dual control model architecture of accelerator/brake balance.
• Arousal: Affected by vascular health (erectile function depends substantially on endothelial function), neurological function, hormonal status (especially oestrogen in women for lubrication), psychological state, and substance use (alcohol impairs arousal at higher doses despite reducing inhibition at lower doses).
• Orgasm: Affected by sufficient stimulation duration and quality, pelvic floor function, neurological function, medications (SSRIs notably delay or prevent orgasm), and substantial individual variation in orgasm threshold.
• Resolution and refractory period: In men, age-dependent (shorter in younger men, longer in older men). Affected by overall health and fatigue. In women, there’s no absolute refractory period; multiple orgasms with brief breaks are physiologically possible.

III. Orgasm: Mechanics, Variation, and What’s Known

The Physiology

Orgasm is a neurological event with consistent physiological signatures: rhythmic contractions of pelvic floor muscles at approximately 0.8-second intervals, contractions of accessory reproductive structures (uterus and vagina in women; prostate, seminal vesicles, and vas deferens in men), substantial autonomic activation (heart rate, blood pressure, respiration), and characteristic neurochemical release (dopamine surge, oxytocin release, prolactin elevation, endorphin release).

The brain activity during orgasm shows distinctive patterns: substantial reduction in lateral orbitofrontal cortex activity (the region associated with executive control and self-monitoring), activation of the ventral tegmental area and nucleus accumbens (the brain’s reward circuitry), and reduced activity in the default mode network (the self-referential thinking network). The pattern overlaps partially with what’s observed during meditative absorption, certain psychedelic states, and other experiences of transcendence.

Variation in Orgasm

• Frequency of orgasm in partnered sex: Survey research consistently shows sex differences. In heterosexual partnered sex, men report orgasm approximately 95% of the time; women report orgasm approximately 65% of the time on average, with variation by relationship type (higher in established relationships, lower in casual encounters). The “orgasm gap” is partly a reflection of anatomical reality (the clitoral structure typically requires direct or targeted stimulation that not all sexual encounters provide), and partly a reflection of cultural and educational factors.
• The orgasm gap in same-sex partnered sex: Women in same-sex partnerships report orgasm frequencies similar to men in same-sex partnerships, suggesting the heterosexual gap is largely about practice rather than physiological capacity. Closing the gap is about what the practice involves rather than fundamental limitations.
• Multiple orgasm: In women, multiple orgasms (additional orgasms within minutes of the first, without returning to baseline) are physiologically possible for most, though not all women. Estimates vary, but approximately 15–30% of women regularly experience multiple orgasms. In men, multiple orgasms are physiologically possible but rare; they typically require separating orgasm from ejaculation through practice (Karezza-style or specific tantric techniques) since the refractory period follows ejaculation rather than orgasm per se.
• Female ejaculation and squirting: Distinct phenomena, sometimes confused. Female ejaculation involves small-volume prostatic-fluid-equivalent secretion from the paraurethral glands. Squirting involves larger-volume expulsion that includes some bladder content. Both occur in some women, particularly with intense anterior vaginal wall stimulation. Neither is a marker of orgasm quality; some women never experience either despite intense orgasms; some experience either or both without intense pleasure.
• Difficulty reaching orgasm (anorgasmia): Affects approximately 10–15% of women regularly and a smaller percentage of men. Often related to insufficient stimulation duration or type, medication effects (SSRIs in particular), psychological factors, or pelvic floor dysfunction. Treatable in most cases.

What Predicts Orgasm in Women

The research on predictors of female orgasm in partnered sex is reasonably detailed:

• Direct clitoral stimulation: Either manual, oral, or with toys. Penetration alone produces orgasm in approximately 25% of women; the addition of direct clitoral stimulation raises rates substantially.
• Adequate stimulation duration: Approximately 13–15 minutes of focused stimulation is the average requirement for women, compared to 2–6 minutes for men. The time to orgasm in women is longer on average and more variable.
• Relationship factors: Women in committed relationships report substantially higher orgasm rates than in casual encounters. Relationship satisfaction, communication, and partner attentiveness all predict orgasm rates.
• Specific practices: Survey research finds that the practices most associated with female orgasm are oral sex, manual stimulation of the clitoris during penetration, deep kissing, and self-stimulation during partnered sex.
• Position effects: Positions that allow clitoral access during penetration (woman-on-top, side-by-side, or modified positions with hand access) typically produce orgasm more reliably than positions without clitoral access.

Closing the orgasm gap in heterosexual partnered sex involves practices that target the clitoral structure, sufficient time, and the relational conditions that support sustained engagement. The cultural emphasis on penetrative sex as the central act produces predictable underperformance on female orgasm.

IV. Practical Techniques With Empirical Support

The technique question is genuinely contested in popular media, with substantial variation between what advice columns recommend and what survey research suggests works. The following techniques are supported by survey research on sexual satisfaction and orgasm rates.

Foreplay

Sufficient foreplay matters more in heterosexual partnered sex than in same-sex or solo sex, primarily because women’s responsive desire patterns and longer time-to-orgasm require longer engagement. Research suggests that approximately 15–20 minutes of foreplay before penetration produces substantially better outcomes than shorter durations, particularly for female orgasm and overall satisfaction.

Effective foreplay involves multiple sensory channels: kissing, manual touch across the body (not just genitals), oral stimulation, verbal communication, and progressive escalation. The “foreplay as a warm-up to the real activity” framing produces worse outcomes than the “foreplay as a substantial portion of the sexual experience” framing.

Manual and Oral Stimulation

Manual stimulation of the clitoris involves engaging both the external glans and the internal structures through pressure applied via the labia majora and the anterior vaginal wall. An effective technique typically involves:

• Adequate lubrication (saliva, lubricant, or arousal-produced)
• Varied pressure and rhythm (sustained light to moderate pressure with rhythmic motion tends to work better than alternating extremes)
• Communication with partner about what’s working
• Sustained engagement rather than brief stimulation

Oral stimulation (cunnilingus) is one of the more reliably orgasm-inducing practices for women in partnered sex, according to survey research. Effective technique involves similar principles: sustained engagement, varied pressure and rhythm, and attention to feedback. The “alphabet” technique (tracing letter shapes with the tongue) is commonly recommended in popular sources, but the research supports more sustained engagement than specific motion patterns.

For male anatomy, manual stimulation of the penis is most effective when it varies pressure, rhythm, and grip; engages the frenulum and glans (where most sensation is located); and isn’t limited to the shaft. Oral stimulation (fellatio) typically benefits from manual stimulation of the shaft simultaneously, attention to the frenulum, and varied depth.

Penetration

Penetrative sex produces orgasm in women at variable rates depending on position and additional stimulation. Penetration alone produces orgasm in approximately 25% of women; penetration with simultaneous clitoral stimulation produces orgasm in a substantial majority.

Position effects on female orgasm:

• Woman-on-top: Allows the woman to control angle, depth, and clitoral contact. Among the higher-orgasm-rate positions.
• Coital alignment technique (CAT): A modified missionary position where the man positions higher on the woman, producing direct clitoral contact during pelvic thrusting. Research suggests improved orgasm rates with this position.
• Side-by-side: Allows hand access to clitoris while penetrating.
• Doggy style: Allows deep penetration; clitoral access requires deliberate hand engagement.
• Modified missionary: Standard missionary with pillow under hips for angle change, plus clitoral hand engagement.

Position selection should track what produces sensation for both partners rather than what’s depicted in pornography. The depicted positions optimise for visual display rather than for the partners’ sensation.

Anal Sex

The anus has substantial nerve density and is sexually responsive in many people of both sexes. Anal sex is reported by approximately 20–30% of heterosexual couples and at higher rates in same-sex male couples.

• The anus lacks natural lubrication. Adequate external lubricant is essential.
• The internal anal sphincter is involuntary; relaxation requires arousal and gentle progression.
• Bacterial transfer to the vagina or urethra causes urinary tract and vaginal infections. Cleaning between anal and vaginal/oral activity is essential.
• HIV transmission risk is higher with receptive anal sex than with other practices; barrier protection substantially reduces this risk.
• Pain during anal sex usually indicates insufficient relaxation, lubrication, or progression speed; sustained pain warrants stopping rather than pushing through.

Sex Toys

Sex toy use is reported by a substantial majority of women and a smaller but substantial percentage of men. 

• Vibrators reliably produce orgasm in women who don’t orgasm easily through other means. Approximately 90% of women who use vibrators report easier orgasm.
• Solo vibrator use can shift orgasm response patterns; some women find that they become dependent on vibrator stimulation and have more difficulty reaching orgasm through other means. This is reversible by temporarily reducing vibrator use.
• Vibrator use during partnered sex (worn or held by partner) is associated with higher female orgasm rates and is reported as relationship-positive by most couples who use them.
• Body-safe materials matter. Silicone, glass, and stainless steel are body-safe. Jelly rubber and PVC can leach phthalates and other endocrine disruptors. Buying from established sex toy retailers with body-safety certification is worth the additional cost.
• Lubricant compatibility varies by toy material. Silicone-based lubricant degrades silicone toys; water-based lubricant works with everything but may need reapplication; oil-based lubricant degrades latex condoms.

Lubrication

Adequate lubrication substantially improves sexual experience for both partners and reduces friction-related discomfort. The dual control model relevance: insufficient lubrication produces brake activation (discomfort, anticipated discomfort, anxiety) that further reduces arousal in a self-amplifying loop.

• Water-based: Most common, compatible with all toys and condoms, may need reapplication. Glycerin-containing water-based lubricants can cause yeast infections in some women.
• Silicone-based: Long-lasting, water-resistant (useful for shower or bath sex), incompatible with silicone toys.
• Oil-based: Long-lasting but degrades latex condoms and diaphragms. Coconut oil is a popular natural option, but it causes problems for some women (microbial disruption).
• Hybrid: Combinations attempting to combine advantages.

Avoid lubricants with parabens, glycerin (in susceptible women), or fragrance for regular use.

V. The Orgasm Gap and Closing It

Heterosexual women in partnered sex report orgasm rates substantially lower than men in the same encounters, lower than women in same-sex encounters, and lower than the same women report during solo sex.

Closing the Gap

The research consistently identifies several factors that substantially close the gap:

1. Direct clitoral stimulation during partnered sex: Manual, oral, or vibrator-assisted. Both before and during penetration. The single largest intervention.
2. Adequate time: Most women require 13–15 minutes of focused stimulation; many require longer. Time pressure and rushed sex produce lower orgasm rates.
3. Communication: Couples who discuss what works produce higher orgasm rates than couples who don’t. The cultural taboo against discussing sex during sex is counterproductive.
4. Variety in practices: Couples who incorporate multiple practices (manual, oral, penetrative, toy-assisted, varied positions) produce higher rates than couples who consistently use the same script.
5. Solo orgasm practice: Women who masturbate to orgasm regularly report higher partnered orgasm rates than women who don’t. Self-knowledge of what works enables effective communication with partners.
6. Partner attentiveness: The research consistently finds that male partners’ attention to female pleasure and willingness to sustain stimulation predict female orgasm rates more than any specific technique.

The cultural script that prioritises penetration and treats male orgasm as the natural endpoint of sex is the source of much of the gap.

VI. Sexual Pain and Dysfunction

In Women

Dyspareunia (painful intercourse): Affects approximately 10–20% of women at some point. Causes include:

• Vaginismus: Involuntary tightening of pelvic floor muscles preventing or making painful any vaginal penetration. Treatable through pelvic floor physiotherapy, graduated dilator therapy, and cognitive-behavioural therapy. Often has psychological components (anxiety, history of painful or traumatic sexual experience) alongside physical components.
• Vulvodynia: Chronic vulvar pain without an identified cause. Diagnosis is partly by exclusion. Treatment includes pelvic floor physiotherapy, topical medications (lidocaine, oestrogen cream), oral medications (gabapentin, antidepressants), and psychological support.
• Vestibulodynia: Pain specifically at the vaginal opening (vestibule). Often responsive to specific treatments including topical medications and surgical intervention in severe persistent cases.
• Endometriosis: Endometrial tissue growing outside the uterus. Can cause deep dyspareunia, particularly with penetration. Affects approximately 10% of women. Diagnosis often delayed by years; surgical excision is the most definitive treatment.
• Insufficient lubrication: Common in perimenopause and menopause due to oestrogen decline. Treatable with local oestrogen therapy and lubricants.
• Pelvic floor dysfunction (hypertonicity): Pelvic floor muscles holding chronic tension. Pelvic floor physiotherapy is the primary treatment; Kegels typically worsen the problem.

Painful sex shouldn’t be tolerated as normal. It substantially predicts relational and psychological consequences when sustained. Pelvic floor physiotherapy is one of the most evidence-supported interventions and is underutilised.

In Men

• Erectile dysfunction (ED): Discussed in detail below. Affects approximately 50% of men over 40 to varying degrees.
• Premature ejaculation: Discussed in detail below. Affects approximately 20–30% of men.
• Delayed ejaculation: Difficulty reaching orgasm despite adequate stimulation. Less common than premature ejaculation, but causes substantial distress when it occurs. Causes include medication effects (particularly SSRIs), nerve damage, and psychological factors.
• Anorgasmia: Inability to reach orgasm. Less common in men than women but occurs. Causes overlap with delayed ejaculation.
• Peyronie’s disease: Fibrous plaque formation in the penis producing painful erection and curvature. Affects approximately 9% of men. Treatable through medications, injections, and surgery in severe cases.

When to Seek Help

For both sexes, sexual difficulties that persist for more than several months and cause distress warrant professional consultation. The primary care provider can rule out medical causes and refer appropriately. Pelvic floor physiotherapists, certified sex therapists, urologists, and gynaecologists all have legitimate roles in addressing different aspects.

VII. Erectile Function: Maintenance, Decline, and Restoration

Erectile function depends on multiple integrated systems: vascular (blood flow into and retention within the penis), neurological (nerve signalling from the brain and spinal cord), hormonal (testosterone supports but doesn’t directly produce erection), and psychological (anxiety, depression, and stress all affect erection).

Physiology

Erection requires arterial inflow exceeding venous outflow, producing the trapping of blood in the corpora cavernosa under pressure. The mechanism involves nitric oxide release from neurons and endothelial cells, smooth muscle relaxation in the corpus cavernosum, and venous compression by the tunica albuginea (the connective tissue surrounding the erectile tissue). Anything that impairs any of these mechanisms can produce erectile dysfunction.

Causes of Erectile Dysfunction

Organic causes (the body):

• Vascular disease: Atherosclerosis affects penile arteries before larger vessels in many men, which is why ED is often the first symptom of cardiovascular disease. The penis has been called the “barometer of cardiovascular health.”
• Diabetes: Affects both vascular and neural components.
• Hormonal deficiency: Low testosterone reduces libido and contributes to ED, though most men with ED have normal testosterone.
• Neurological disease: Multiple sclerosis, spinal cord injury, prostate surgery, pelvic surgery.
• Medications: Many antidepressants, antihypertensives, antihistamines, and other common medications affect erectile function.
• Smoking: Vascular damage; reversible to a degree if quit early enough.
• Excessive alcohol: Both acute and chronic effects.
• Obesity: Multiple mechanisms including vascular, hormonal, and metabolic.

Psychogenic causes (the mind):

• Performance anxiety: The brake activation pattern from the dual control model.
• Depression: Affects desire and arousal through multiple pathways.
• Relationship difficulties: Conflict, resentment, or attachment insecurity.
• Trauma history

Mixed: Most men with ED have a combination of organic and psychogenic factors. The two reinforce each other: organic difficulties produce performance anxiety, which produces further difficulty, which produces more anxiety.

Treatments

• Lifestyle interventions: The largest effect sizes for erectile improvement come from cardiovascular health interventions: exercise, weight loss, blood pressure control, blood sugar control, smoking cessation, alcohol reduction. A 2011 meta-analysis found that lifestyle interventions produce erectile improvement effect sizes comparable to medication in many men.
• PDE5 inhibitors: Sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), avanafil (Stendra). Inhibit phosphodiesterase type 5, prolonging nitric oxide effects and supporting erection. Highly effective for most men with ED. Side effects include headache, flushing, dyspepsia, nasal congestion, and rarely vision changes. Tadalafil’s longer half-life produces a more “natural” pattern of being available rather than needing timing. Daily low-dose tadalafil is well-tolerated by most men and produces improvement.
• Testosterone replacement: Only effective for men with clinically low testosterone. Doesn’t help ED in men with normal testosterone levels and may cause cardiovascular concerns in some men. Should only be initiated by physicians after appropriate workup.
• Vacuum erection devices: Produce erection through negative pressure. Constriction ring at the base maintains erection. Effective for many men but less convenient than oral medications.
• Intracavernosal injections: Direct injection of medication (alprostadil, papaverine, phentolamine) into the corpora cavernosa. Highly effective. Used by men who don’t respond to oral medications.
• Penile prostheses: Surgical implants. Used in cases not responsive to other treatments. Effective and durable but irreversible.
• Pelvic floor exercises: Modest but real effect on erectile function, particularly in younger men. The pelvic floor muscles contribute to erection maintenance.
• Psychological intervention: Cognitive-behavioural therapy, sensate focus protocols, sex therapy. Particularly relevant for primarily psychogenic ED and for the psychological component of mixed ED.

Maintaining Erectile Function with Age

Most men experience some decline in spontaneous erection frequency and ease with age. The pattern is gradual rather than sudden in most men without specific medical insults.

Sustaining erectile function across decades:

• Maintain cardiovascular health aggressively.
• Avoid smoking entirely.
• Moderate alcohol intake.
• Maintain healthy body composition.
• Address sleep issues including sleep apnoea.
• Maintain regular sexual activity (use it or lose it has empirical support for erectile function).
• Address erectile difficulties early rather than avoiding them.

VIII. Premature Ejaculation and Ejaculation Control

Premature ejaculation (PE) affects approximately 20–30% of men. Definition varies but commonly involves ejaculation within 1 minute of penetration, inability to delay ejaculation as desired, and associated distress.

Causes

Approximately equal contributions from biological and psychological factors:

• Biological: Penile sensitivity, serotonin receptor function, genetic predisposition.
• Psychological: Anxiety, conditioning patterns from solo sex (rushing to orgasm), relationship factors.

Treatments

• Behavioural techniques: The stop-start technique (stopping stimulation as ejaculation approaches, resuming when arousal subsides) and the squeeze technique (compressing the glans as ejaculation approaches) have moderate empirical support and can be practised solo to develop awareness of arousal levels.
• Pelvic floor exercises: Specific exercises strengthening the bulbocavernosus and ischiocavernosus muscles can improve ejaculatory control.
• Topical anaesthetics: Lidocaine sprays and creams reduce penile sensitivity and substantially extend time to ejaculation. Side effects include reduced sensation and potential transfer to partner.
• SSRIs: Selective serotonin reuptake inhibitors delay ejaculation as a side effect. Used off-label for PE. Dapoxetine is a short-acting SSRI specifically developed for on-demand PE treatment, available in some countries.
• Tramadol: An opioid with serotonin and norepinephrine effects. Delays ejaculation. Used with caution due to addictive potential.
• PDE5 inhibitors: Combined with SSRIs in some treatment protocols.
• Sex therapy: Combination of behavioural techniques, anxiety management, and relationship work.

Ejaculation Control as Skill

Some men practice ejaculation control as a deliberate skill, separating orgasm from ejaculation through techniques drawn from Taoist and tantric traditions. The Karezza protocol involves sustained sexual activity without ejaculation; some men report intense sensations and ability to maintain extended sessions. The empirical research is limited, but the techniques are well-established in their traditions. Most men can extend ejaculation latency with deliberate practice using the techniques above.

IX. Hormonal Health: Real Effect Sizes

The hormonal layer affects sexual function but operates as one input among several. Effect sizes for various interventions are smaller than the wellness industry suggests.

Testosterone

What raises testosterone:

• Treating diagnosed hypogonadism with TRT: Restores normal levels. The intervention with the largest effect.
• Sleep optimisation: 5h sleep restriction reduces testosterone by 10–15% in young men; recovery sleep restores levels.
• Resistance training: Acute spike of 15–30% post-session lasting 24–48 hours; sustained programmes produce modest baseline improvements particularly in men with sedentary baseline.
• Body fat reduction: In overweight or obese men, weight loss of 10kg+ can increase testosterone by 20–40%.
• Sufficient zinc, vitamin D, magnesium: In men with deficiency, correction improves testosterone modestly (5–15%). In men with adequate levels, additional supplementation produces minimal effects.
• Reducing chronic stress: Sustained high cortisol reduces testosterone; effective stress management can produce modest improvements.
• Specific supplements: Tongkat ali (~10–15% increase at adequate dose in men with subclinically low levels), ashwagandha (modest effects), boron (modest effects in some studies). Most other “testosterone boosters” produce minimal effects.

What lowers testosterone:

• Sleep deprivation
• Excessive endurance training (>75 min sessions chronically)
• Severe caloric restriction
• Excessive alcohol
• Obesity
• Type 2 diabetes
• Chronic stress
• Opioid use (substantial suppression)
• Many medications (statins modestly, glucocorticoids substantially)
• Endocrine disruptors (phthalates, BPA, atrazine) — cross-referenced from The Environmental Rabbit Hole

Oestrogen

In women, oestrogen affects vaginal lubrication, tissue health, mood, sleep, cognition, cardiovascular health, and bone density. The natural decline through perimenopause and menopause produces real changes that are addressable through hormone replacement therapy when warranted.

In men, oestrogen (derived from aromatisation of testosterone) plays roles in brain function, libido, and bone health. Excessively low oestrogen in men produces problems, including reduced libido and poor bone health. The “man boobs from too much oestrogen” framing in popular biohacker sources often misunderstands the underlying physiology: gynecomastia results from testosterone-to-oestrogen ratio imbalance, not absolute oestrogen elevation.

What the Wellness Industry Oversells

Most “testosterone boosters” produce effects under 5% in men with normal levels. Many produce no measurable effect at all. The combination supplements sold for “male vitality” rarely contain effective doses of any active ingredient and frequently make unsupported claims.

Red light therapy on genitals for testosterone elevation: speculative.

Specific supplement protocols claimed to dramatically transform hormonal status: typically marginal effects.

Lifestyle fundamentals produce 80%+ of available hormonal optimisation. Supplements produce small additional effects. Specific medical interventions (TRT, HRT) produce large effects but should be appropriately prescribed and monitored.

X. Hormone Replacement: What’s Justified

Female Hormone Replacement

The Women’s Health Initiative (WHI) study published in 2002 produced a shift in attitudes toward hormone replacement therapy for menopausal women. The initial reports suggested elevated breast cancer and cardiovascular risk. Subsequent analyses revised this picture: the risks were primarily in older women starting HRT well after menopause; women starting HRT close to menopause (within 10 years) showed neutral or positive cardiovascular effects and modest breast cancer risk elevation only with combined oestrogen-progesterone, not oestrogen alone.

Reasonable HRT considerations:

• For symptom relief: Hot flashes, night sweats, mood disturbance, sleep disruption, vaginal atrophy. HRT is the most effective treatment for menopausal symptoms. Topical/vaginal oestrogen for genitourinary symptoms has minimal systemic effects and is appropriate for most women regardless of systemic HRT decisions.
• For bone protection: Particularly in early menopause and in women at elevated osteoporosis risk.
• Cardiovascular considerations: Women starting HRT within 10 years of menopause show neutral or modestly positive cardiovascular outcomes. Women starting more than 10 years post-menopause may face elevated cardiovascular risk.
• Cancer considerations: Combined oestrogen-progesterone produces small absolute increase in breast cancer risk. Oestrogen-only therapy in women without uterus shows minimal breast cancer effect.
• Bioidentical vs synthetic: “Bioidentical” usually means molecularly identical to endogenous human hormones. Most FDA-approved HRT preparations now use bioidentical oestradiol and progesterone. Compounded bioidentical hormones marketed by wellness practitioners typically have weaker quality control without demonstrated additional benefit.

Male Testosterone Replacement Therapy (TRT)

For men with clinically low testosterone (typically <300 ng/dL with symptoms), TRT is effective and well-supported. For men with normal testosterone seeking enhancement, TRT carries cardiovascular risks without commensurate benefit.

Reasonable TRT considerations:

• Diagnosis requires multiple morning measurements: showing consistently low testosterone alongside clinical symptoms.
• Forms include injections, topical gels, patches, pellets, and oral preparations: Injections produce more fluctuation; topical gels more steady levels.
• Monitoring requires regular blood work: for testosterone levels, haematocrit (red blood cell concentration that rises with TRT and can cause clotting risk), prostate-specific antigen (PSA), and lipid markers.
• Fertility consideration: TRT suppresses endogenous testosterone production and impairs sperm production. Men who want to preserve fertility need alternative approaches (clomiphene, hCG, others).
• Cardiovascular questions: The cardiovascular safety of TRT has been contested in the past decade. Recent research suggests neutral cardiovascular effects when properly prescribed and monitored in men with genuine hypogonadism.
• Long-term implications: TRT is typically lifelong once started, since endogenous production suppression can persist after cessation.

The wellness industry’s promotion of TRT for men with normal testosterone substantially exceeds the evidence base and carries genuine risks. TRT belongs in clinical practice with appropriate diagnosis and monitoring.

XI. Fertility: Sperm Quality, Egg Quality, and Age

Sperm Quality

Modifiable factors affecting sperm count, motility, and morphology:

• Heat exposure: Hot baths, saunas, laptops on lap, tight underwear, prolonged sitting. All reduce sperm count and quality. Effects reverse within 2–3 months of removing exposure.
• Smoking: Substantial effect on sperm DNA fragmentation and motility.
• Alcohol: Heavy drinking reduces sperm quality; moderate drinking has minimal effects.
• Cannabis: Reduces sperm count and motility.
• Obesity: Reduces testosterone-to-oestrogen ratio and sperm quality.
• Stress: Modest effects on sperm quality.
• Nutrition: Adequate zinc, selenium, antioxidant intake supports sperm quality. Mediterranean dietary patterns associated with better sperm parameters.
• Exercise: Moderate exercise associated with better sperm quality; excessive endurance training reduces it.
• Endocrine disruptors: Phthalates, BPA, pesticides. Cross-referenced from The Environmental Rabbit Hole.
• Age: Sperm quality declines gradually after age 35–40. Offspring of older fathers show modest elevations in some neurodevelopmental conditions.
• Frequency of ejaculation: Daily ejaculation maintains better sperm quality than weekly; weekly better than monthly. The “save it up for better sperm” intuition is wrong; sperm sitting in storage degrade.

Egg Quality and Female Fertility

Egg quality declines more dramatically with age than sperm quality. Women are born with their full lifetime supply of eggs; the supply diminishes through ovulation and atresia (natural egg loss) across the reproductive lifespan.

• Age effects: Fertility peaks in the 20s, declines modestly through early 30s, more rapidly after 35, and dramatically after 40. By 43, fertility is substantially reduced, and the proportion of chromosomally abnormal eggs is high.
• Modifiable factors: Smoking accelerates ovarian ageing. Severe over- or undereating disrupts ovulation. Diabetes affects egg quality. Endocrine disruptor exposure may affect egg quality. Most other interventions produce modest effects on egg quality.
• Egg freezing: Practical option for women who want to delay childbearing. Effectiveness depends substantially on age at freezing; earlier (before 35) produces better outcomes.
• The fertility decline is real and unavoidable in unmodified form: The cultural pattern of delayed childbearing in industrialised societies meets the biological pattern of accelerating fertility decline producing the contemporary fertility difficulties many couples experience.

Combined Considerations

The sperm decline picture covered in The Environmental Rabbit Hole (Swan’s Count Down, Skakkebæk’s testicular dysgenesis syndrome work) operates alongside individual modifiable factors. Population-level sperm count declines suggest environmental and lifestyle factors are operating across populations; individual men can affect their own sperm quality through the modifiable factors above.

Couples experiencing fertility difficulties: testing both partners is essential. Approximately 30% of fertility issues are primarily male factor, 30% primarily female factor, 30% combined, 10% unexplained. The cultural pattern of focusing fertility workup primarily on the woman misses male factor contributions.

XII. Contraception: Comparative Effectiveness

Contraception effectiveness varies substantially by method. The effectiveness numbers most often quoted are perfect-use rates; typical-use rates are usually lower.

Method Effectiveness (Typical Use, First Year)

• Implants (Nexplanon): >99% effective. Lasts 3 years. Hormonal (progestin). Side effects include irregular bleeding patterns.
• IUDs:
  
  • Copper IUD (Paragard). >99% effective. Lasts 10–12 years. Non-hormonal. May increase menstrual bleeding and cramping.
  • Hormonal IUDs (Mirena, Kyleena, others). >99% effective. Lasts 3–8 years depending on type. Local progestin with minimal systemic effects. Often reduces menstrual bleeding.
• Sterilisation:
  
  • Vasectomy. >99% effective. Permanent (some reversible cases). Outpatient procedure.
  • Tubal ligation. >99% effective. Permanent. Surgical procedure.
• Injectables (Depo-Provera): 94% effective. Every 3 months. Hormonal. Side effects include bone density reduction with long-term use.
• Combined hormonal contraceptives (pill, patch, ring): 91% effective. Daily, weekly, or monthly use. Hormonal effects on multiple systems.
• Progestin-only pill (minipill): 91% effective. Daily use. More forgiving of timing than combined pill.
• Diaphragm with spermicide: 88% effective.
• Male condom: 87% effective (typical use; 98% perfect use). Provides STI protection.
• Withdrawal (pull-out): 78% effective (typical use). Higher than commonly assumed because perfect-use is approximately 96%.
• Fertility awareness methods: 76–88% effective depending on method and discipline. Some methods (symptothermal) are more effective than others (calendar only).
• Spermicide alone: 72% effective.

The Hormonal Contraception Question

Hormonal contraceptives (combined pills, patches, rings, injections, implants, hormonal IUDs) have well-documented effects beyond contraception:

• Mood effects: Approximately 5–15% of women experience mood changes with hormonal contraception. Some experience improvement (particularly with PMDD); some experience worsening. Effects are often dose-dependent.
• Libido effects: Hormonal contraception reduces free testosterone by elevating sex hormone binding globulin (SHBG). The effect produces reduced libido in some women.
• Cardiovascular effects: Combined hormonal contraceptives elevate clot risk modestly. The absolute risk is small but elevated in smokers, women over 35, and those with clotting disorders.
• Cancer effects: Modest reductions in ovarian and endometrial cancer risk; modest increases in breast and cervical cancer risk.
• Bone density: Depo-Provera reduces bone density particularly with long-term use; reversible after discontinuation.
• Microbiome effects: Hormonal contraception affects vaginal and possibly gut microbiome.

Hormonal contraception is effective and well-tolerated by most women, but the effects beyond contraception are real and warrant attention to whether the specific person is among those who experience adverse effects.

The Non-Hormonal Options

Copper IUD, condom, diaphragm, fertility awareness, and male sterilisation all avoid hormonal effects while providing varying degrees of effectiveness. Copper IUD is particularly underused given its high effectiveness and long duration.

XIII. Sexually Transmitted Infections

Screening Recommendations

The standard screening framework (US CDC, adapted for general guidance):

• Annual: for sexually active people under 25 or with new partners: chlamydia, gonorrhoea, HIV.
• More frequent: for higher-risk situations (multiple partners, unprotected sex, sex work): quarterly to semi-annual screening.
• Syphilis screening: for pregnant women and higher-risk populations.
• Hepatitis B and C: screening based on risk factors.
• HPV: Cervical cancer screening for women per age-appropriate guidelines.
• HIV: At least once in lifetime for all adults; more frequently for higher-risk populations.

The Major STIs

• Chlamydia: Often asymptomatic. Treatable with antibiotics. Untreated can cause pelvic inflammatory disease, infertility, ectopic pregnancy. Screen regularly in younger sexually active populations.
• Gonorrhoea: Similar pattern. Antibiotic resistance increasing.
• HPV: Many strains; some cause genital warts, some cause cancers (cervical, anal, oropharyngeal). Vaccination (Gardasil 9) prevents most cancer-causing and wart-causing strains. Vaccinate before sexual debut for maximum effectiveness; remains beneficial in already-active adults up to age 45.
• Herpes (HSV-1 and HSV-2): Lifelong infection. Most carriers asymptomatic. Daily antiviral suppression reduces transmission and outbreaks. HSV-1 (typically oral but increasingly genital) and HSV-2 (typically genital).
• HIV: Lifelong but manageable with antiretroviral therapy. Pre-exposure prophylaxis (PrEP) reduces transmission risk in higher-risk populations. Treatment as prevention: people with an undetectable viral load cannot transmit.
• Syphilis: Treatable with antibiotics. Untreated can cause serious systemic disease.
• Hepatitis B: Vaccination is the primary prevention. Sexually transmissible.
• Trichomoniasis: Treatable. Often asymptomatic in men; symptomatic in women.

Barrier Protection

Condoms substantially reduce transmission of most STIs when used consistently and correctly. Effectiveness is highest for fluid-borne pathogens (HIV, gonorrhoea, chlamydia) and lower for skin-contact pathogens (HPV, herpes), though still substantial for the latter.

Dental dams protect oral-vaginal or oral-anal sex.

Pre-Exposure Prophylaxis (PrEP)

Daily oral or injectable medication for HIV-negative people at elevated HIV risk. Highly effective (>99% with daily adherence). Underutilised in eligible populations.

Communication

The cultural pattern of avoiding STI discussions in new sexual situations produces preventable transmission. Asking about testing status and sharing your own status before sexual contact is reasonable and appropriate, not awkward or unromantic in a meaningful sense.

XIV. Sex Across the Lifespan

Adolescence

Sexual development through puberty. First experiences vary by culture and individual development. Most adolescents would benefit from accurate, comprehensive sexuality education that abstinence-only frameworks fail to provide. Sex education that includes contraception and consent reduces pregnancy and STI rates without increasing sexual activity rates.

Twenties

Peak fertility, generally high sexual function, and often relational instability. The cultural pattern of delayed partnership formation extends this period. Sexually transmitted infection risk peaks in this period due to partner change frequency.

Thirties

Fertility begins declining in women (more sharply after 35). Many people transition to long-term partnerships and families. The challenges of long-term sexual partnership become operative: declining frequency, the desire-intimacy paradox, and the integration of parenting and sexual life.

Forties

Fertility decline continues. Many women begin experiencing perimenopausal symptoms. Erectile difficulties become more common in men. Long-term partnership dynamics continue operating.

Fifties and Beyond

Menopause typically in the early 50s in women. Continued erectile decline in men. Sexual frequency typically declines, but satisfaction can remain high with appropriate adjustments. Some couples report deeper sexual satisfaction in this period because the early intensity has been replaced by a more skilled and attuned partnership.

What Sustains Sexual Function with Age

• Maintaining cardiovascular health
• Maintaining hormonal health
• Maintaining the relationship
• Maintaining sexual activity (use it or lose it has empirical support)
• Addressing difficulties early rather than avoiding them
• Adapting to changing function rather than expecting unchanged function

XV. Sex During Pregnancy, Postpartum, and Through Hormonal Transitions

Pregnancy

Sex during pregnancy is safe in uncomplicated pregnancies until labour. Position adjustments accommodate the growing abdomen. Many women experience changes in libido during different trimesters (often increased in the second trimester, variable in the first and third).

Avoid penetrative sex in cases of:

• Placenta previa
• Cervical incompetence
• History of preterm labour
• Vaginal bleeding
• Ruptured membranes

Postpartum

The standard recommendation is to wait approximately 6 weeks after birth before resuming penetrative sex, particularly after vaginal birth or C-section. The actual recovery time varies; some women experience extended sexual difficulties.

Common postpartum sexual issues:

• Vaginal dryness due to lactational oestrogen suppression
• Pelvic floor dysfunction (laxity from vaginal birth; sometimes hypertonicity)
• Body image changes
• Fatigue
• Reduced libido (multiple causes including hormones, sleep deprivation, role transition)
• Pain from healing tears or episiotomy
• Cesarean recovery considerations

Pelvic floor physiotherapy in the postpartum period substantially improves outcomes and is underutilised.

Perimenopause and Menopause

Symptom management is covered above in Hormone Replacement. Sexual implications include:

• Vaginal atrophy (treatable with local oestrogen)
• Reduced libido (treatable with appropriate hormone management)
• Sleep disruption affecting overall function
• Mood changes
• Body image changes

Local vaginal oestrogen has minimal systemic effects and is appropriate for most postmenopausal women regardless of systemic HRT decisions.

Andropause

The gradual decline of testosterone in men with age, sometimes called andropause, though the term is misleading because the pattern is gradual rather than abrupt. Some men experience symptomatic low testosterone in their 40s-60s; many maintain adequate testosterone throughout life. Symptoms warranting evaluation include reduced libido, fatigue, mood changes, reduced muscle mass, and erectile difficulties.

XVI. Sex With Chronic Illness or Disability

Sexual function is affected by many chronic conditions, and adaptations make sexual life possible across most conditions. Common conditions with sexual implications:

• Cardiovascular disease: Often produces ED (which can be the first symptom). Sexual activity is safe for most cardiac patients; the typical exercise demand of sex is moderate.
• Diabetes. Affects vascular and neural function. Both men and women may experience reduced sensation, lubrication, or erectile function. Glycaemic control supports sexual function.
• Multiple sclerosis: Variable effects on sexual function depending on disease pattern and location of demyelination.
• Spinal cord injury: Substantial effects on sexual function. Many adaptations are available. The Sexuality Information and Education Council of the United States and similar organisations provide specific guidance.
• Cancer treatments: Surgery, chemotherapy, and radiation all affect sexual function. Many cancer treatment programmes now include sexual rehabilitation.
• Chronic pain conditions: Affect desire and capacity. Pacing strategies and position adjustments support continued sexual activity.
• Mental health conditions: Depression, anxiety, and PTSD all affect sexual function. Treatment of the underlying condition often improves sexual function; medication side effects can complicate the picture.

Sexual life is typically possible with chronic illness or disability, though it often requires adaptation, partner communication, and willingness to engage professional support when needed.

XVII. Medication Effects on Sexual Function

Many common medications affect sexual function. Patients often don’t connect their medication to sexual changes; physicians often don’t proactively discuss this. Common offenders:

• SSRIs: Reduce libido, delay or prevent orgasm in 30–60% of users. Bupropion is an antidepressant with less sexual side effect profile.
• Antipsychotics: Reduce libido and arousal; some elevate prolactin, which compounds the effect.
• Antihypertensives: Beta-blockers and thiazide diuretics affect erectile function. ACE inhibitors and angiotensin receptor blockers have lower sexual side effect profiles.
• Statins: Modest effects on libido and erectile function in some users.
• Antihistamines: Reduce lubrication.
• Opioids: Substantial suppression of testosterone in men; reduced libido in both sexes.
• Benzodiazepines: Reduce libido and arousal.
• Hormonal contraceptives: Discussed above.
• 5-alpha-reductase inhibitors (finasteride, dutasteride, used for hair loss and BPH): Sexual side effects in approximately 5–15% of users; post-finasteride syndrome with persistent effects after discontinuation reported in a smaller percentage.

If you’re experiencing sexual function changes that coincide with starting a medication, discuss this with the prescribing physician. Many medications have alternatives with different side effect profiles.

XVIII. Pornography: The Empirical Picture

What’s well-supported:

• Population-level pornography use has increased substantially with internet access.
• Heavy regular pornography use is associated with reduced sexual satisfaction in partnered relationships, particularly when not shared with a partner.
• Pornography use as primary or only sexual education produces specific patterns (the “sexual autism” framing from Heying & Weinstein in Sex Basics).
• Adolescent pornography exposure substantially shapes subsequent sexual expectations, often unrealistically.
• Some users develop tolerance patterns requiring more extreme content for a similar effect, mirroring addiction patterns.

What’s contested:

• Whether pornography use causes erectile dysfunction in young men (porn-induced ED) is contested. Some research supports it; some doesn’t.
• Whether pornography use causes specific sexual behaviour changes (the documented rise in choking, anal sex, and other practices in heterosexual encounters) reflects pornography exposure or other cultural factors.
• The line between problematic and non-problematic use is genuinely unclear.

What the wellness industry oversells:

• Strong “pornography is destroying men’s sex lives” framings often exceed evidence.
• Specific “no-fap” claims about dramatic testosterone elevations from porn cessation are not well-supported.
• Both abstinence-only and “porn is fine for everyone” framings oversimplify.

The reasonable position:

• Heavy pornography use, particularly in adolescents and partnered adults using it instead of partner sex, is associated with negative outcomes.
• Occasional use in adults with healthy partnered sex appears to have minimal negative effects for most users.
• The cultural pattern of pornography as primary sexual education is producing population-level effects that deserve attention.
• Individual users vary substantially in their relationship to pornography; what’s problematic for one user may not be for another.

XIX. Masturbation: Effects and Frequency

Masturbation is essentially universal in men and very common in women. The cultural pattern of treating it as shameful or harmful has weak empirical support.

• Frequency: Substantial individual variation. The “normal” range in healthy adults extends from rare to daily; nothing in the empirical research suggests any specific frequency is harmful unless it interferes with daily function.
• Effects on testosterone: Minimal. The Jiang 2003 study suggested a small transient rise at day 7 of abstinence, returning to baseline. Long-term ejaculation frequency has minimal effect on basal testosterone.
• Effects on prostate health: Higher ejaculation frequency is associated with lower prostate cancer risk in some research.
• Effects on partnered sex: Masturbation in partnered adults generally doesn’t reduce partner sex; the two correlate positively in most research.
• Effects on relationship quality: Solo masturbation by partnered adults is generally relationship-neutral; the perception that it’s harmful is more often the relationship problem than the masturbation itself.

The “no-fap” community’s specific claims about masturbation causing testosterone reduction, motivation loss, and other dramatic effects are not well-supported by the empirical research. The community sometimes conflates pornography use (which has documented effects) with masturbation per se (which does not).

Masturbation is normal, generally healthy, and beneficial in many ways, including stress relief, sleep improvement, sexual self-knowledge, and pelvic floor exercise. Patterns that interfere with function (compulsive use, replacement of partnered sex when desired, escalating to harmful content) warrant attention; ordinary use does not.

XX. Casual Sex Outcomes

What’s documented:

• A fraction of casual sex encounters produce regret or negative emotion, particularly for women. Men report regret at lower rates and more often regret missed opportunities than acted-on ones.
• Casual sex doesn’t reliably produce psychological harm in adults who consciously choose it, but it doesn’t reliably produce benefit either.
• Specific patterns (drunken hookups, regrettable encounters, sex without consent or boundary clarity) produce worse outcomes than other patterns.
• The asymmetry in oxytocin/vasopressin response (covered in Optimizing Pleasure) produces predictable patterns of relational mismatch.
• Population-level shifts toward normalised casual sex correlate with delayed partnership formation, declining marriage rates, declining birth rates, and elevated reported loneliness across multiple Western populations.

What’s contested:

• The mental health effects of casual sex on the individuals involved.
• Whether the population-level patterns reflect causation by casual sex norms or other factors.
• Whether the current cultural defaults are improvements over previous restrictions.

What’s reasonable:

• Consensual sex between adults is none of anyone else’s business as a moral matter.
• Casual sex can be neutral, positive, or negative for the individuals involved, depending on many factors.
• The aggregate cultural shift toward casual sex as the default mating pattern has produced documentable patterns that include reduced relationship satisfaction in populations that have most thoroughly adopted it.
• Individual practice and cultural patterns are different things.

XXI. Kink, BDSM, and Non-Standard Practices

A substantial minority of adults engage in BDSM (bondage, discipline, dominance, submission, sadism, masochism) or related practices. 

• BDSM practitioners do not show elevated rates of psychopathology compared to the general population.
• Some research suggests BDSM practitioners show modest psychological well-being advantages on some measures.
• The neurobiology of some BDSM practices (intense sensation, altered states) overlaps with documented effects of meditation, intense exercise, and other practices that produce flow states.
• Consent practices in established BDSM communities are typically more explicit and elaborated than in mainstream sexual practice, which is one reason these communities show lower rates of consent violations than the general population on some measures.

Kink practices that are consensual between adults, involve appropriate safety practices, and don’t interfere with overall function are not pathological and don’t require treatment. Practices that are compulsive, harmful, non-consensual, or interfere with function warrant clinical attention regardless of whether they involve kink content.

XXII. Open Relationships and Polyamory

Approximately 4–5% of adults in research samples report being in some form of consensual non-monogamous (CNM) relationship at a given time, with substantially higher numbers reporting interest or past experience.

• Relationship satisfaction in CNM relationships is comparable to that of monogamous relationships on average.
• Specific subtypes (swinging, open relationships, polyamory) show somewhat different patterns.
• Communication demands are higher in CNM relationships; couples who maintain them successfully report substantial communication skill development.
• Risk of relationship dissolution may be modestly higher than in monogamous relationships, though the research is limited.
• STI rates are not higher than in serial monogamous populations when CNM practitioners follow safer-sex protocols.
• Children raised in polyamorous family structures show outcomes comparable to children in two-parent monogamous structures in the limited available research.

CNM is a viable relationship structure for some couples; it requires more communication and emotional skill than monogamy; it isn’t a solution for failing monogamous relationships; the outcomes depend substantially on the specific people involved.

XXIII. Sexual Orientation and Identity

The research on sexual orientation has produced a fairly consistent picture:

• Heritability: Twin studies suggest moderate genetic contribution to sexual orientation, particularly in men. Specific genes have proven elusive in genome-wide association studies, suggesting many small contributions rather than single major genes.
• Prenatal hormonal exposure: Multiple lines of evidence suggest prenatal androgen exposure patterns contribute to sexual orientation development.
• The fraternal birth order effect: The likelihood of being gay in men rises modestly with each older brother born to the same mother, possibly through maternal immune response patterns to male foetal antigens.
• Sexual orientation is largely set early in development: The reparative or conversion therapy approaches that claim to change orientation are not supported by evidence and produce documented harm.
• Sexual orientation may be more fluid in women than men on some measures: Lisa Diamond’s longitudinal research has documented this pattern.
• Approximately 4–6% of adults identify as gay or lesbian: Approximately 2–4% identify as bisexual. The total LGB population is approximately 7–10% depending on measurement.

Sexual orientation has biological components, develops early, isn’t reliably changeable through therapy, and isn’t pathological. The cultural debates about the origins and meaning of sexual orientation are partly distinct from the empirical questions about its development and stability.

XXIV. What Doesn’t Work

Penis enlargement:

• Pills, creams, devices: no evidence base for permanent enlargement.
• Traction devices: modest temporary effects; substantial sustained use required for any persistent gain; risk of injury.
• Surgery: high complication rates; modest results; not recommended for cosmetic purposes by most reputable urologists.
• The popular framing that men “need” enlargement overstates the partner-relevance of length over girth.

“Manhood enhancement” supplements:

• Most testosterone boosters: minimal effects in men with normal levels.
• Most libido enhancers: marginal effects.
• “Sexual stamina” supplements: limited evidence.
• The combination products typically contain inadequate doses of any active ingredient.

Female enhancement products:

• Most “libido boosters” for women: limited evidence.
• “Vaginal tightening” creams: ineffective; pelvic floor physiotherapy is the evidence-based approach.
• Most “intimacy” products: marketing rather than substance.

Surgical interventions for cosmetic reasons:

• Labiaplasty (cosmetic): complication risk; questionable benefit.
• “Vaginal rejuvenation” (laser or surgical): limited evidence; substantial costs.
• Most penile surgeries for non-medical reasons: risk; marginal benefit.

Many “tantric” and “biohacking” sex protocols:

• Many extravagant claims have limited empirical support.
• Some legitimate techniques (sensate focus, mindfulness-based interventions) are preserved in some traditions but overlaid with claims that exceed evidence.
• The “biohacking the bedroom” protocol categories from popular wellness sources typically combine some sensible interventions with speculation.

“Pheromone” perfumes and colognes:

• The human pheromone framework is contested as covered in Optimizing Pleasure.
• The commercial products claiming to use human pheromones have minimal evidence base.

Most products sold for sexual enhancement produce minimal effects. The interventions that produce effects are:

• Treating underlying medical conditions
• Lifestyle fundamentals (cardiovascular health, sleep, body composition, stress management)
• Hormone replacement when clinically indicated
• Medications for specific dysfunctions (PDE5 inhibitors for ED, etc.)
• Pelvic floor physiotherapy for many sexual difficulties
• Sex therapy and couples therapy for relational and psychological factors
• Communication and relational work

XXV. Cross-Links

The conceptual framing for sex (the “becoming one” framework, pleasure as motivation and meaning as goal, the population vs individual distinction) is in Sex Basics.

The detailed biological substrate (chromosomal architecture, hormonal profiles, sexual dimorphism across systems, the cognitive sex differences picture) is in Biological Sex.

The relational architecture of sustained sexual satisfaction (dual control model, attachment, desire-intimacy paradox, affective neuroscience) is in Optimizing Pleasure.

The foetal sexual development, intersex conditions, sexual orientation research, and contested empirical territories are in The Sex Rabbit Hole.

The endocrine disruption material affecting reproductive health is in The Environmental Rabbit Hole and The Elements. The sleep and circadian biology supporting hormonal health is in Sleep & Circadian Rhythm. The movement and exercise effects on hormones are in Movement. The nutrition and microbiome effects are in Nutrition.