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.
What is an Anal Fissure?
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.
Symptoms of Anal Fissure
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.
Cardinal Symptoms
- Severe pain during bowel movements — often described as sharp, cutting, or like 'passing broken glass'. This is the most consistent and debilitating symptom.
- Prolonged burning or throbbing pain after bowel movements — lasting anywhere from 30 minutes to several hours after the bowel movement has concluded. This is characteristic of anal fissure and less typical of haemorrhoids.
- Bright red rectal bleeding — typically a small amount on the surface of the stool, on the toilet paper, or in the toilet bowl. Not mixed into the stool.
Other Symptoms
- A visible crack or tear in the skin around the anus
- A small skin tag (sentinel pile) at the lower end of the fissure — often mistaken for a haemorrhoid
- Anal itching or irritation
- Fear of defecation — a cycle develops in which the patient consciously or subconsciously delays bowel movements to avoid pain, leading to harder stools and worsening the fissure
Causes and Risk Factors
Primary causes
- Passage of large, hard stools — the most common cause; tearing from trauma during difficult defecation
- Constipation and straining — increased effort during defecation increases mechanical stress on the anal mucosa
- Prolonged or severe diarrhoea — repeated passage of liquid stool can traumatise and macerate the anal mucosa
- Childbirth — especially following a prolonged second stage of labour or perineal tears; anterior fissures are more common in this setting
Secondary Causes (Atypical Fissures)
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:
- Crohn's disease: Bowel inflammation can affect the perianal area, causing fissures that are often atypical in appearance and location
- HIV and other immunodeficiency states: Impair tissue healing and increase susceptibility to opportunistic perianal infections
- Sexually transmitted infections: Syphilis, gonorrhoea, and chlamydia can cause or mimic perianal conditions
- Anal cancer: A fissure that does not heal or has an atypical appearance requires tissue sampling to exclude malignancy
Risk Factors
- Infant and young child: High water content of stools decreases in infancy; anal fissures are common in infants aged 6–24 months
- Young to middle-aged adults: The most common affected age group for primary fissures
- Pregnancy and postpartum: Constipation in pregnancy and vaginal delivery are both risk factors
- Low-fibre diet and inadequate hydration: Producing hard, difficult-to-pass stools
- Inflammatory bowel disease: Particularly Crohn's disease
- Prior anal surgery: Scarring may affect the blood supply and healing capacity of the anal canal
Preventing Anal Fissures
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.
- Maintain a high-fibre diet: Aim for 25–30 grams of dietary fibre daily from fruits, vegetables, wholegrains, and legumes
- Drink adequate fluids: 6–8 glasses of water daily to ensure soft, formed stools
- Respond to the urge to defecate promptly — delaying causes stools to harden
- Avoid prolonged sitting on the toilet: This increases pelvic floor strain and anorectal pressure
- Treat constipation early: Do not allow constipation to persist without addressing it
- After childbirth: Maintain a high-fibre diet and stool softeners in the postpartum period to reduce straining
- Protect the anal area: After diarrhoeal illness, use gentle patting rather than wiping, and apply a barrier cream to protect the anal skin
How is an Anal Fissure Diagnoses
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.
- Clinical History: The pattern of pain (during and after bowel movements), bleeding (bright red, on paper or in bowl), duration, and associated symptoms is usually sufficient to make a confident clinical diagnosis of anal fissure.
- External Inspection: Gentle examination of the perianal skin often reveals the fissure directly — a linear tear at the posterior midline (or anterior in postpartum women), sometimes with a sentinel pile. A formal internal examination is deferred until healing allows
- Anoscopy: Examination of the anal canal using a short, wide-bore tube (anoscope). Performed under local anaesthetic cream. Identifies the fissure, its extent, the presence of haemorrhoids, and other anorectal pathology. Not always required if the diagnosis is clear on clinical grounds.
- Colonoscopy: Not routinely required for straightforward anal fissure. Indicated when: rectal bleeding is unexplained or significant, a change in bowel habit is present, age and risk factors warrant colorectal cancer screening, or an atypical fissure raises concern for IBD or other pathology.
- Anorectal Manometry: Measures internal anal sphincter resting pressure. Typically elevated in chronic anal fissure (sphincter hypertonia). Used in specialist settings to guide treatment — patients with very high resting pressures may be good candidates for sphincterotomy; those with low pressures are not.
- Examination Under Anaesthesia (EUA): Formal examination of the anal canal under general or spinal anaesthesia. Used when pain or spasm prevents adequate examination in the clinic, or as the first step of a surgical procedure.
