Anal fissure: the paper-cut pain with a very effective fix
Last updated September 3, 2026.
An anal fissure is a small tear in the lining of the anal canal, and its pain is famously out of proportion to its size: a sharp, tearing, glass-like pain during and after passing stool, sometimes with bright red blood. Most fissures follow constipation or a hard stool, and most heal within weeks once the cycle of tearing and muscle spasm is broken. It is common, it is not serious, and it is very treatable.
What does it feel like?
A sharp, cutting pain as stool passes, often followed by a deep burning ache lasting minutes to hours afterward, sometimes with bright red blood on the paper or streaking the stool. The fear it creates is the engine of the problem: anticipating the pain, people hold in stool, which makes it harder, which tears the fissure open again. Some people get a small skin tag at the fissure's edge (the sentinel pile). The pain is severe enough that many sufferers assume something sinister; the pattern is reassuringly typical.
Why does it happen?
Usually mechanical: a hard, constipated stool (or a bout of diarrhea) tears the lining, and the internal anal sphincter then spasms in response, clamping down, reducing blood flow to the tear, and preventing healing: a pain-spasm-poor-healing loop. Childbirth, anal intercourse, and chronic constipation are common contexts. Fissures off the midline, multiple, painless, or non-healing raise the question of other causes (Crohn's, infection) and get investigated rather than just treated.
What actually heals it?
- Soften the stool: the foundation: fiber (25-30g daily) plus fluids, and a stool softener (like a macrogol laxative) while healing; the goal is soft stools that pass without stretching.
- Warm baths: sitting in warm water for 10-20 minutes (especially after bowel movements) relaxes the spasm and soothes; genuinely evidence-supported comfort.
- Do not hold back: go when the urge comes; delaying hardens the next stool and re-tears the fissure.
- Spasm-relaxing ointments: for fissures not healing in a few weeks: GTN or diltiazem ointment (prescription) relaxes the sphincter and restores blood flow, healing most chronic fissures over 6-8 weeks (headache is the common GTN side effect).
- For the stubborn: Botox injection into the sphincter or a minor surgical procedure (lateral sphincterotomy) for fissures that defeat ointments, with high success rates.
When is it an emergency?
Anal fissures are routine care. The patterns that need a different look: heavy or persistent bleeding (more than streaks and drips), blood mixed through the stool rather than on it, fever with anal pain or a throbbing lump (an abscess: same-day), a discharge of pus, unintentional weight loss or a change in bowel habit (especially over 40: rectal bleeding then needs proper assessment), and fissures that are multiple, off to the side, or painless. Any severe worsening pain with inability to pass urine also goes in urgently. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does something so small hurt so much?
Because the anal canal is one of the most densely innervated areas of the body (the same sensitivity that gives you control makes tears exquisitely painful), and because of the spasm loop: the tear triggers the internal sphincter to clamp, which both hurts directly and starves the tear of the blood supply it needs to heal, so the pain is the injury plus the muscle reaction to it. This also explains the treatments: everything effective either softens what passes through or relaxes that spasm. The severity of the pain is characteristic, not a sign of something worse.
Is the blood a worry?
In the fissure pattern, no: bright red blood streaking the stool or spotting the paper, separate from the stool, accompanying the sharp pain, is typical of fissures (and hemorrhoids). The blood patterns that change the conversation: blood mixed through the stool, darker or maroon blood, heavy bleeding, blood with mucus, and any rectal bleeding accompanied by a change in bowel habit, weight loss, or anemia symptoms, especially over 40, all of which need proper assessment because they point higher up the bowel. When the pattern is the classic fissure one, the blood is the tear bleeding, and it stops as the tear heals.
How long until it heals?
Acute fissures (under six weeks) mostly heal within days to a few weeks once stools soften: the constipation fix is genuinely the treatment. Chronic fissures (beyond six weeks, often with a visible tag and a rolled edge) rarely heal with softening alone, because the spasm loop is established: they respond to the spasm-relaxing ointments (GTN or diltiazem, 6-8 weeks, healing 50-70% of chronic cases), then Botox or the small surgical procedure for the remainder, which succeeds in the great majority. The arc depends entirely on breaking the cycle early: the fissure treated in week one rarely meets the surgeon.
What actually keeps stools soft enough?
The working recipe: 25-30 grams of fiber daily (fruit, vegetables, wholegrains, or a fiber supplement like psyllium if the diet falls short), 1.5-2 liters of fluid (fiber without water backfires into harder stools), and, during healing, a stool softener or osmotic laxative like a macrogol (polyethylene glycol), which is gentle, non-habit-forming, and the standard companion. Toilet habits matter as much: go when the urge arrives (delay hardens stool), do not strain or linger (no phone on the toilet), and a footstool under the feet straightens the passage. Keep the routine after healing; recurrence follows the return of constipation.
What are GTN and diltiazem ointments, and what should I expect?
Prescription ointments applied just inside the anal canal twice daily for 6-8 weeks that relax the internal sphincter, restoring blood flow so the fissure can heal: GTN (glyceryl trinitrate) works in roughly half to two-thirds of chronic fissures, with headache the common side effect (a pea-sized amount, a finger cot, and tolerance building over days manage it); diltiazem works similarly with less headache and has become many clinicians' first choice. They are the middle rung: stronger than softening alone, short of surgery. If a full proper course fails, the sphincter-relaxing minor surgery has the highest success rate of all.
When is a fissure not just a fissure?
The atypical features that earn investigation: fissures off the midline (typical ones sit at 6 or 12 o'clock), multiple fissures, painless fissures, fissures that will not heal despite correct treatment, and fissures with other symptoms (diarrhea, mouth ulcers, weight loss, abdominal pain: the Crohn's pattern). In those, the tear is a sign rather than the disease, and the workup (examination, sometimes biopsy or bowel imaging) looks for Crohn's disease, infection, and, rarely, other causes. A typical, painful, midline fissure after constipation in an otherwise well person is what it looks like; the atypical list is the reason non-healing fissures always go back for review.