Anal fissure — the complete guide

An anal fissure is a small tear in the lining of the anus. It hurts disproportionately to its size, often heals on its own with the right routine, and is one of the most common reasons people end up reading articles like this one.

What is an anal fissure?

The anal canal is lined by sensitive tissue. When stool stretches it beyond its tolerance — usually by being too hard, too forceful, or too frequent — the lining can tear. That tear is a fissure. Most are at the back of the canal (the posterior midline), where blood supply is naturally weaker, which is also why fissures heal more slowly than tears elsewhere on the body.

Two unhelpful things tend to happen at the same time. First, the tear is exposed to stool every time you go. Second, the internal sphincter — a ring of involuntary muscle — goes into protective spasm. Spasm reduces blood flow, blood flow is what heals tissue, and the cycle becomes self-sustaining. This is why "just wait it out" doesn't work past a certain point.

Symptoms

The classic pattern is sharp, tearing pain during a bowel movement, often described as "passing glass," followed by a lingering deep burning ache that can last minutes to hours. Most people see bright red blood on the toilet paper or the surface of the stool. Itching is common as healing starts. Some people develop a small skin tag at the outer end of the fissure — the sentinel pile — which is a sign of chronicity, not a separate problem.

What people often don't realize is how much fissures affect quality of life. Anticipation of pain leads to constipation, constipation leads to harder stool, harder stool leads to more pain. Many people start avoiding meals before a known toilet time, dread their morning routine, and lose sleep — all from a tear smaller than a grain of rice.

Causes

Most fissures come from passing hard stool — the leading risk factor by a wide margin. Other triggers include explosive diarrhea (which whips through the canal at force), childbirth (postpartum fissures are extremely common), and any anal trauma. A small minority of fissures are caused by underlying conditions like Crohn's disease, ulcerative colitis, infection, or — rarely — cancer. Atypical features (off-midline, multiple, painless, non-healing) raise the suspicion of something underlying.

Diagnosis

A clinician will usually diagnose a fissure on visual inspection alone — gently parting the buttocks reveals the tear in most cases. Internal exams (digital, anoscopy) are often deferred during an acute fissure because they're so painful. If the picture isn't typical or the fissure isn't healing, further evaluation is warranted to rule out infection, inflammatory bowel disease, or rare malignancy.

Home treatment — the foundation

Most acute fissures heal in 4–6 weeks with consistent conservative care. The four pillars:

1. Stool softening

Aim for soft, formed, easy-to-pass stool. The targets:

• Fiber: 25–35 grams per day, increased gradually over 5–7 days to avoid bloating. Psyllium husk is the most studied supplement — 1 teaspoon twice daily in water is a reasonable starting dose.
• Water: More than you currently drink. Fiber without fluid hardens stool — exactly the opposite of the goal.
• Osmotic laxative: A PEG-based laxative (Miralax, Movicol) for 1–2 weeks during the worst phase is gentle and effective.

2. Sitz baths

Warm-water sitz baths are the single most underrated treatment. They relax the internal sphincter — the same muscle whose spasm is preventing healing. 10–15 minutes, 2–3 times a day, especially after every bowel movement. Plain warm water works as well as anything fancy.

3. Topical numbing

An over-the-counter or prescription anesthetic (lidocaine 2–5%) applied 15–20 minutes before a bowel movement can dramatically reduce the worst spike of pain.

4. Toilet habits

Don't hold stool when you have the urge. Don't strain. Don't sit for more than 5 minutes — a footstool that raises your knees toward your chest brings the anorectal angle to a more open position.

Prescription topicals

If conservative care isn't producing improvement after 4–6 weeks, prescription topical agents are the next step. Both target the sphincter spasm directly.

Diltiazem is generally preferred when available because it has fewer side effects and similar efficacy.

Chronic fissures

Once a fissure has been around longer than 6–8 weeks and the wound has become chronic, the chance of healing with conservative care alone drops. Persistent symptoms beyond this point usually warrant either:

1. Botulinum toxin injection — paralyzes the sphincter for 2–3 months, allowing healing. Outpatient procedure, no incision. Healing rates around 60–70%; recurrence is possible.
2. Lateral internal sphincterotomy (LIS) — the surgical gold standard. A small, controlled cut in the internal sphincter releases the spasm permanently. Healing rates above 90%. The trade-off is a small risk of incontinence, which is why surgeons individualize the depth of the cut.

Procedures & surgery

For most patients with a chronic fissure, the conversation with a colorectal specialist will compare Botox versus LIS. LIS has the highest cure rate of any treatment but a real (if uncommon) risk of mild flatus or stool incontinence. Botox is reversible, has no incontinence risk, but a higher recurrence rate. The right choice depends on your continence, age, prior obstetric history, and tolerance for recurrence.

Read more: Surgery options & recovery

Recovery from procedures

Recovery from LIS is typically faster than people expect — most patients return to desk work within 5–7 days. The first few bowel movements are uncomfortable but improve quickly. Sitz baths, soft stool, and pain control during week one make the biggest difference. Full healing timeline →

Preventing recurrence

The single biggest predictor of a recurrence is going back to the bowel habits that caused the first fissure. Long-term:

• Maintain dietary fiber and hydration. Don't drop the new habits when the pain stops.
• Treat constipation early — don't let hard stools become a pattern.
• Use a footstool. Keep toilet visits short.
• Get postpartum fissures evaluated promptly; don't normalize ongoing pain.

When to see a doctor

You should see a clinician if:

• Symptoms persist beyond 6–8 weeks despite consistent conservative care
• The fissure is off-midline, painless, or has unusual features
• You have Crohn's disease or another reason to think the fissure is secondary
• Bleeding is heavy, dark, or accompanied by other symptoms (weight loss, change in bowel habit)
• You have a fever or signs of infection

Full red-flags guide →

Common questions