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How the anus actually works
It isn't one muscle, and it isn't a mystery: two sphincters manage continence, the skin is richly innervated, and the discomfort around this body part has a traceable history — not a biological basis.
- The anal sphincters
The anus is the end of the digestive tract, and it isn't one muscle — it's two rings, one inside the other. The internal sphincter is smooth muscle, the same kind of automatic tissue as the gut itself: it stays closed on its own, without effort or instruction. The external sphincter is skeletal muscle — the same kind as the muscles you move deliberately. It's mostly under voluntary control, and it's the last line when you need to hold on until a better moment.
Continence is what the two rings produce together: no accidental leaks, and the decision about when to release is yours. An urge typically follows the same sequence. Stool fills the rectum, the wall stretches, and the internal sphincter reflexively relaxes — an involuntary step known as the rectoanal inhibitory reflex. Then the choice arrives: you either relax the external sphincter, or you keep it contracted and wait. How much filling it takes to feel a clear urge varies from person to person.
What this isn't
- It isn't a storage bag. The anal canal itself — the short passage the sphincters guard — typically doesn't hold stool; stool waits higher up, and the lower rectum may hold a small amount temporarily, depending on how long it's been since you last went and how much there is. 'Usually nothing waiting at the door' is accurate; 'always empty' is not.
- And variation isn't a defect. Sensitivity, resting tone, and how firmly the sphincters close all differ from person to person, and they change with age, childbirth history, surgery, and health conditions. Those are normal differences in a working body part, not faults.
Where this comes from
The uneasiness many people feel about this body part has a traceable history — including in the language of anatomy itself. The pudendal nerve takes its name from the Latin pudere, a root usually translated as 'to be ashamed.' Some etymology scholars argue the root's meanings were broader — closer to respect and modesty — and the International Federation of Associations of Anatomists has been reviewing whether terms derived from it should be retired. Either way, the word carries a long history of discomfort, stamped into the terminology itself.
The rest of the taboo comes from the usual places: the association with excrement, religious teachings, and the assumption that this region belongs to someone else's sexuality. Those are cultural layers, not properties of the tissue. The psychology of shame has its own article — this one sticks to how the part works.
The skin of this region is richly innervated. Below the dentate line — roughly the lower part of the anal canal — the area is supplied by somatic sensory nerves, which is why it's sensitive to touch, temperature, and stretch.
Much of that supply travels through the pudendal nerve, which typically arises from the sacral roots S2–S4 and gives off three main branches: one to the anal region, one to the perineum, and one to the genitals. The anus and the genitals therefore share part of their nerve supply — with wide normal variation from person to person in how the branches run. Shared supply describes anatomy; it doesn't decide what anything will feel like.
The 'automatic vs. on-command' split between the two sphincters is a division of labor, not two absolute categories. The external sphincter also carries an involuntary baseline tone, and anal tone more broadly is regulated by spinal mechanisms and modulated by context — it isn't a fixed setting.
Under stress, this region can tighten without your asking it to. In small lab experiments, healthy volunteers showed involuntary pelvic-floor and perianal muscle activity while watching threat- or anxiety-inducing film clips, and clinical observations record similar anticipatory tightening in people with pelvic pain conditions — before anything even touches them. The reverse oversimplification doesn't hold either: at rest, pelvic-floor tone doesn't simply track how anxious someone is, and mental load can weaken voluntary sphincter control rather than just clamp everything tighter. Individual differences are large — you may notice your own patterns if you pay attention, but there's no single universal pattern to match.
Two gates, two kinds of control
| Type | Muscle type | How it's controlled | Its default state | Its job in continence |
|---|---|---|---|---|
| Internal sphincter | Smooth muscle — the same automatic tissue as the gut wall. | Involuntary. It works on reflex, without instruction or effort. | Closed by default. It relaxes reflexively when the rectum fills and stretches. | Holding the line around the clock — preventing accidental leakage. |
| External sphincter | Skeletal muscle — the same deliberately movable kind as in your arms and legs. | Mostly voluntary, though it also carries an involuntary baseline tone — 'automatic vs. on-command' is a tendency, not two absolute categories. | Ready to contract on purpose. It's the muscle you clench when you need to wait. | The last line — the when and where of release stays your decision, until you make it. |
Myth & reality
The anus is the most nerve-dense part of the body — basically a built-in pleasure switch.
The skin of the anal region is richly innervated and genuinely sensitive to touch, temperature, and stretch — that much is true. But 'most dense' or 'second most dense' rankings have no reliable measurements behind them. And a rich nerve supply cuts both ways: the same touch can feel pleasant, neutral, or uncomfortable depending on how it's done and the state you're in.
Studies of painful anal stimulation find the pain associated with things like insufficient lubrication, lack of arousal, and anxiety — context, not just wiring. Sensation thresholds also vary a lot from person to person.
Why it matters
Treating sensitivity as a promise sets expectations the body never agreed to — and when the promised magic doesn't arrive, the discomfort gets read as personal failure or a broken body part, instead of as information.
Stimulation there is a gay men's thing.
Everyone has an anus, and in broad terms it's built and supplied much the same way for everyone — with normal individual variation in the details. Whatever meaning a culture attaches to this region, anatomy doesn't assign it to one orientation.
Why it matters
Attaching shame to identity keeps straight and queer people alike from understanding a part of their own bodies — and keeps a stereotype in circulation.
A bad first experience means this part just doesn't work for me.
How stimulation here feels depends heavily on how it happens and in what context — lubrication, arousal, tension, and the ability to relax all shape it. Pain and strong discomfort are signals to stop and adjust, not a verdict on the body part. Even with good preparation, you may simply not enjoy it — that's valid information too, and a perfectly fine outcome.
Why it matters
Turning one signal into a lifetime verdict closes off both adjusting the approach and asking for help — the two things that actually change experience.
What's normal, what's worth adjusting, what's worth a clinician's input
Sensitivity, resting tone, and continence vary widely between people, and they shift over a lifetime — with age, childbirth, surgery, and health conditions. Variation is normal, not a defect to fix.
Discomfort and pain during intimacy are signals to respect, not prices to pay. If something hurts, stopping and adjusting is the correct response — not endurance. And 'I tried it carefully and didn't like it' is a complete, valid answer: this article explains a body part, it doesn't make a case for exploring it. Choosing not to is as normal as choosing to.
Understanding the anatomy and still feeling uneasy about it is also normal — unease has a psychological history that anatomy alone can't settle. If past experiences, pain, hemorrhoids, or anal fissures are part of your picture, they don't necessarily rule out comfort forever — but they belong with a qualified clinician, not with an article.
Sources
Educational references for the research described above. They do not endorse this article, and they do not replace professional medical advice.
- Lee, J. M., & Kim, N. K. (2018) — Essential Anatomy of the Anorectum for Colorectal Surgeons Focused on the Gross Anatomy and Histologic Findings. Annals of Coloproctology, 34(2), 59–71.
Surgical-anatomy review: the internal sphincter as smooth muscle, the external sphincter as somatically supplied striated muscle; below the dentate line, innervation by the inferior rectal nerve makes the area sensitive.
- Mittal, R. K., & Tuttle, L. J. (2022) — Anorectal Anatomy and Function. Gastroenterology Clinics of North America, 51(1), 1–23.
Review of anorectal anatomy and function: external sphincter and puborectalis as striated muscle with distinct architecture, working with the smooth-muscle internal sphincter to maintain continence.
- Kadam-Halani, P. K., Arya, L. A., & Andy, U. U. (2017) — Clinical anatomy of fecal incontinence in women. Clinical Anatomy, 30(7), 901–911.
Clinical-anatomy review: continence is maintained by coordination of the sphincter complex with sensation, rectal compliance, and voluntary control — and varies with age, parity, and pelvic-floor status.
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- Amarenco, G., Kerdraon, J., Chesnel, C., Desprez, C., Le Breton, F., Sheikh Ismael, S., Turmel, N., Haddad, R., & Hentzen, C. (2020) — Anal tone: Physiology, clinical and instrumental characteristics. Progres en Urologie, 30(11), 588–596.
Review of anal tone physiology: regulation depends on spinal segmental mechanisms under supra-sacral control; tone alterations are context-dependent and can be behavioral without pathological significance.
- Carrington EV, Heinrich H, Knowles CH, et al. (2020) — The international anorectal physiology working group (IAPWG) recommendations: Standardized testing protocol and the London classification for disorders of anorectal function. Neurogastroenterology and Motility, 32(1), e13679.
International consensus protocol: the rectoanal inhibitory reflex is a standard, testable reflex; minor findings such as anal hypertension can be present in healthy people.
- De Ocampo, S., Remes-Troche, J. M., Miller, M. J., & Rao, S. S. (2007) — Rectoanal sensorimotor response in humans during rectal distension. Diseases of the Colon and Rectum, 50(10), 1639–1646.
Experimental study in 23 healthy subjects: all showed rectoanal reflexes; the volume needed to feel fullness and the desire to defecate varied, with urge responses growing at higher volumes.
- Shafik, A., Ali, Y. A., & Afifi, R. (1997) — Is the rectum a conduit or storage organ?. International Surgery, 82(2), 194–197.
Study of 48 healthy volunteers: stool was palpable in the lower rectum in a majority, depending on time since last defecation — the rectum can hold a small amount between voids.
- Schubert, M. C., Sridhar, S., Schade, R. R., & Wexner, S. D. (2009) — What every gastroenterologist needs to know about common anorectal disorders. World Journal of Gastroenterology, 15(26), 3201–3209.
Review stating directly that the anoderm is richly innervated and sensitive to touch, temperature, and stretch because of somatic nerve supply.
- Yang, J., Webb, K. E., Carrington, E. V., Cullen, E. M., Digesu, A., Everaert, K., Ibrahim, A., Kemp, H., Mears, A., Panicker, J. N., & Drake, M. J. (2026) — Anatomical Variation of the Pudendal Nerve and Related Structures. European Urology Open Science, 85, 71–81.
Scoping review: the pudendal nerve typically arises from S2–S4 and gives off inferior rectal, perineal, and dorsal genital branches — shared origin for anal and genital supply, with substantial individual variation.
- Nercessian, T. R., Banbury, S., & Chandler, C. (2023) — A Systematic Review Looking at Anodyspareunia Among Cisgender Men and Women. Journal of Sex & Marital Therapy, 49(7), 829–841.
Systematic review of 8 studies: painful anal stimulation was associated with anxiety, lack of lubrication, lack of stimulation, and lack of arousal — correlates, not causes; evidence centered on MSM and cisgender women.
- van der Velde, J., & Everaerd, W. (2001) — The relationship between involuntary pelvic floor muscle activity, muscle awareness and experienced threat in women with and without vaginismus. Behaviour Research and Therapy, 39(4), 395–408.
Film-induction experiment: involuntary pelvic-floor muscle activity rose during threat and sexual-threat excerpts (and not during neutral or erotic ones), including in the small healthy comparison group.
- Hannan-Leith, M. N., Dayan, M., Hatfield, G., Lalumiere, M. L., Albert, A. Y., & Brotto, L. A. (2019) — Is Pelvic Floor sEMG a Measure of Women's Sexual Response?. Journal of Sexual Medicine, 16(1), 70–82.
Pilot study of 15 sexually healthy women: perianal and intravaginal muscle activity increased during both erotic and anxiety-inducing films.
- McLean, L., Antonio, F. I., Rodrigues, M. P., & Pukall, C. (2025) — Pelvic floor muscle activation in response to pressure stimuli applied to the vulvar vestibule: an observational study comparing women with and without provoked vestibulodynia. Journal of Sexual Medicine, 22(7), 1158–1172.
Observational study: external anal sphincter activation was elevated in anticipation of pressure among women with provoked vestibulodynia — anticipatory tightening before any touch.
- Thubert, T., Deffieux, X., Jousse, M., Guinet-Lacoste, A., Ismael, S. S., & Amarenco, G. (2015) — Influence of a distraction task on pelvic floor muscle contraction. Neurourology and Urodynamics, 34(2), 139–143.
Experiment in 20 healthy volunteers: a mental distraction task made voluntary external sphincter contractions slower and weaker — mental load can reduce control rather than only increase tension.
- Knight, S., Luft, J., Nakagawa, S., & Katzman, W. B. (2012) — Comparisons of pelvic floor muscle performance, anxiety, quality of life and life stress in women with dry overactive bladder compared with asymptomatic women. BJU International, 109(11), 1685–1689.
Case-control study: resting pelvic-floor sEMG baselines were not correlated with anxiety scores — resting tone doesn't simply track anxiety.
- Moxham, B., Pais, D., Plaisant, O., & Kramer, B. (2026) — Moving beyond the use of anatomical terms derived from the Latin word pudere — An opinion piece. Annals of Anatomy, 264, 152773.
Anatomical-terminology history: pudere is conventionally rendered 'to be ashamed'; the IFAA has recommended reviewing pudere-derived terms in Terminologia Anatomica.
- Zdilla, M. J. (2021) — The pudendum and the perversion of anatomical terminology. Clinical Anatomy, 34(5), 721–725.
Historical analysis arguing the root pudere carries broader meanings — respect, modesty, honor — and that translating it only as 'shame' takes the root out of context.
Disclaimer
This article is for adult sex education only. It does not replace professional medical advice. If you have health concerns, please consult a qualified healthcare provider.