The mechanism is a vicious circle, and understanding it explains the whole condition. A hard or large stool tears the delicate lining of the canal. The tear causes pain, and the pain makes the internal sphincter muscle go into spasm. That spasm reduces blood flow to the area and pulls the edges of the tear apart, which stops it healing and sets up more pain with the next bowel movement. Breaking this cycle, the tear, the spasm, the poor blood supply, is the goal of every treatment.

What causes an anal fissure?

Most fissures come from the passage of a hard stool, usually linked to constipation, straining and a low-fibre diet. Bouts of diarrhoea can do it too. Less commonly, childbirth or other conditions are involved. The full set of triggers is covered on the anal fissure causes page.

Acute versus chronic

This distinction matters more than any other. An acute fissure is recent and usually heals with simple measures. A chronic fissure, one that has persisted beyond about six weeks, has often developed firmer edges and that entrenched muscle spasm, so it needs treatment aimed specifically at the spasm.

Symptoms

The classic triad is sharp, knife-like or burning pain during a bowel movement, lingering pain afterwards that can last hours, and a small amount of bright red blood. Many patients begin to dread going to the toilet. The full picture is on the anal fissure symptoms page, and the bleeding in particular is discussed under anal fissure bleeding.

How fissures are treated

Most acute fissures heal with measures that soften the stool and relax the muscle, the foundation of fissure treatment. When a fissure becomes chronic, modern options target the spasm directly, ranging from minimally invasive laser treatment to the established surgical techniques compared on the anal fissure surgery page.

When to see a doctor

See a surgeon if the pain is severe, if a fissure has not healed within a few weeks, or if bleeding is new or recurrent. Bleeding should never be assumed to be a fissure, because other conditions can look similar, including hemorrhoids, which share the bright red bleeding but typically without the sharp tearing pain.

How an anal fissure is diagnosed

The diagnosis is often suspected from the description alone, because the pattern is so characteristic: sharp, tearing pain during a bowel movement, a lingering ache for hours afterwards, and a small amount of bright red blood. A gentle examination confirms it. The reason an assessment still matters is that bleeding has several possible sources, and a fissure should be confirmed rather than assumed, the same caution set out on the anal fissure bleeding page. An experienced clinician also notes whether the fissure looks fresh or has the firm edges and skin tag of a long-standing one.

Acute and chronic: why the distinction drives everything

No single fact matters more in fissure care than whether the tear is acute or chronic. An acute fissure is fresh, with clean edges and reversible spasm, and the great majority heal with simple measures. A chronic fissure, one that has persisted beyond about six weeks, has developed firm edges, scarring and entrenched muscle spasm, so it rarely heals on stool softening alone and needs treatment aimed directly at the muscle. The same tear, caught at different stages, calls for quite different treatment, which is why this distinction frames the whole condition.

The treatment ladder, from sitz baths to surgery

Fissure treatment climbs a clear ladder. The first rung suits almost every acute fissure: softer stools through fibre and fluids, warm sitz baths and an end to straining, the foundation described on the treatment page. When a fissure becomes chronic, the next rungs target the spasm, through medical therapy and then, if needed, a procedure. Minimally invasive laser treatment and the established surgical techniques compared on the surgery page sit at the top. The aim throughout is to relieve the spasm and restore blood flow so the tear can heal, while protecting continence.

Fissures in pregnancy and after childbirth

Fissures are common around pregnancy and delivery, driven by the constipation that pregnancy hormones encourage and the strain of childbirth itself. They often arrive at the most demanding time, yet they respond to the same gentle, safe measures that heal any acute fissure, with treatment choices in pregnancy made carefully by your doctor. This particular situation is covered on the anal fissure in pregnancy and after birth page.

Preventing fissures from returning

Because the original trigger is usually a hard stool, prevention comes down to keeping stools soft for the long term, through adequate fibre, good hydration and an end to straining. These habits matter as much after a fissure has healed as during treatment, since a return of constipation is the commonest reason fissures recur. The triggers worth addressing are set out on the causes page.