An anal fissure is a small tear in the thin, moist mucosa lining the anal canal. It is one of the most painful conditions a person can experience — the sharp, burning pain during and after a bowel movement is characteristically severe and can persist for hours, causing many people to dread going to the toilet and inadvertently delay bowel movements, which makes the problem worse.
Anal fissures are common, affecting people of all ages, and are almost always benign. They are frequently misattributed to haemorrhoids and go untreated for longer than necessary. Effective treatments exist at every stage — most acute fissures heal with conservative management alone, while chronic fissures respond well to specific medical or surgical treatment.
The anal canal is the short passage connecting the rectum to the anus, approximately 2–4 cm long. It is lined by sensitive mucosal tissue and surrounded by two muscle rings — the internal anal sphincter (smooth muscle, involuntary) and the external anal sphincter (skeletal muscle, under voluntary control). The internal sphincter maintains resting anal pressure and is responsible for continence at rest.
An anal fissure is a linear tear in this mucosal lining — most commonly at the posterior midline (the 6 o'clock position), where the blood supply is least rich and the tissue is most susceptible to tearing. In women, anterior fissures are also common following childbirth.
When a fissure occurs, the exposed muscle underneath triggers a reflexive spasm of the internal anal sphincter. This spasm is protective in the short term but counterproductive to healing: it compresses the blood vessels supplying the fissure, reducing the oxygen and nutrient delivery that the tissue needs to repair itself. This sphincter spasm — high resting anal pressure — is the central mechanism that turns an acute fissure into a chronic one.
The distinction between acute and chronic anal fissure is clinically important because the treatment approach and the likelihood of spontaneous healing differ significantly.
| Feature | Acute Fissure | Chronic Fissure |
| Duration | Less than 6–8 weeks | More than 6–8 weeks without healing |
| Appearance | Fresh, clean edges — a simple mucosal tear | Indurated (hardened) edges; fibrous base; often a sentinel pile (external skin tag) at lower end and a hypertrophied anal papilla at upper end — the 'fissure triad' |
| Internal sphincter | Spasm present but reversible | Persistent hypertonia (high resting pressure) impairs blood supply and prevents healing |
| Likelihood of healing | 60–80% with conservative management alone | Unlikely without specific medical or surgical treatment to relax the sphincter |
| Primary treatment | Sitz baths, dietary fibre, stool softeners, topical anaesthetic | Topical nitrates, topical calcium channel blockers, or botulinum toxin injection; lateral internal sphincterotomy for refractory cases |
| Typical cause | Hard stool, straining, childbirth injury | Usually arises from acute fissure that failed to heal; perpetuated by sphincter spasm |
The 'fissure triad' — the characteristic appearance of a chronic fissure — consists of the fissure itself with indurated edges, a sentinel pile (a small flap of redundant skin at the lower end of the fissure, sometimes mistaken for a haemorrhoid), and a hypertrophied anal papilla at the upper end. When all three are present, the diagnosis of chronic anal fissure is essentially confirmed on clinical examination.
The symptoms of an anal fissure are distinctive and, when present together, are usually enough for an experienced clinician to make a confident clinical diagnosis.
A small proportion of anal fissures occur in atypical locations (lateral, anterior without prior childbirth history, or multiple fissures) or fail to respond to standard treatment. These may indicate an underlying condition:
Anal fissures and haemorrhoids are frequently confused by patients — both cause rectal bleeding and perianal discomfort. They are, however, distinct conditions with different clinical features, examination findings, and treatments. The single most useful distinguishing feature is the character and timing of pain.
| Feature | Anal Fissure | Haemorrhoids (Piles) |
| Pain character | Severe, sharp, burning pain during and immediately after bowel movements; 'sitting on glass' | Dull ache or discomfort; prolapsed piles can cause significant pain, especially if thrombosed |
| Pain timing | During and 30 minutes to several hours after defecation | Pain timing During and 30 minutes to several hours after defecation During defecation or with prolonged sitting; less characteristically after bowel movements |
| Bleeding | Bright red, on surface of stool or toilet paper; not mixed in stool | Bright red; typically drips after passing stool; may be splashed in toilet bowl |
| Visible finding | A tear or crack in the anal skin; may see a sentinel skin tag | Swollen vascular cushions, often visible at the anus (external) or felt during digital examination (internal) |
| Itch | Less common | Common — anal pruritus is characteristic of haemorrhoids |
| Prolapse | No | Internal haemorrhoids may prolapse with straining |
| Mucus discharge | No | May occur with prolapsed haemorrhoids |
Both conditions can coexist in the same patient. Clinical examination — and anoscopy where indicated — is required to make an accurate diagnosis. Do not assume the cause of rectal bleeding without a medical assessment.
Diagnosis is primarily clinical — based on the characteristic history of severe post-defecation pain and rectal bleeding. Most anal fissures are visible on gentle external inspection of the anus, without requiring an internal examination, which patients with active fissures find very painful.
Most anal fissures arise from mechanical trauma to the anal mucosa by hard or large stools. Addressing the conditions that produce these stools is the most effective prevention.
