At a glance
Most people associate anal fissures with constipation and hard stools. While this is the most common cause, fissures can develop from a range of other factors. Understanding these less-discussed causes helps explain why some fissures develop without an obvious constipation history and why some require different management approaches.
Causes beyond constipation
Diarrhoea
Frequent diarrhoea is an underappreciated cause of anal fissures. The mechanism is different from constipation:
- Repeated passage of liquid stool irritates and erodes the anal lining
- Acidic stool content damages tissue
- Frequent wiping causes friction and further damage
- The anal canal does not get time to heal between episodes
People with IBS-D, inflammatory bowel disease, or chronic diarrhoea from other causes are at risk.
Childbirth
Vaginal delivery places significant pressure on the perineum and anal area:
- The pushing stage stretches the tissue
- Instrumental delivery (forceps, vacuum) increases the risk
- Tears can extend into the anal area
- Postpartum constipation (from iron supplements, dehydration, fear of straining) compounds the problem
Postpartum fissures are common but often go undiagnosed because attention is focused on the delivery recovery.
Inflammatory bowel disease
Crohn’s disease in particular is associated with anal fissures that behave differently from typical fissures:
- May occur in atypical locations
- May be multiple or broader than usual
- May not respond to standard treatments
- May be accompanied by other perianal disease
Reduced blood flow
Conditions that reduce blood supply to the anal area can make the tissue more vulnerable to tearing and less able to heal:
- Peripheral vascular disease
- Diabetes (particularly when poorly controlled)
- Smoking (which affects microvascular blood flow)
Trauma
Direct trauma to the anal area can cause fissures:
- Anal intercourse (particularly without adequate preparation or lubrication)
- Medical procedures (colonoscopy, banding, other endoscopic procedures)
- Foreign body insertion
Hypertonic sphincter
Some people have a naturally higher resting sphincter pressure (hypertonia) that reduces blood flow to the anal lining. This creates conditions where even normal stool can cause tearing. The sphincter spasm is the primary issue rather than the stool consistency.
Medication effects
Some medications contribute to fissure risk:
- Opioids — cause constipation, the most common medication-related factor
- Isotretinoin — used for acne, associated with mucosal dryness including the anal area
- Chemotherapy agents — can affect mucosal integrity
- Iron supplements — cause constipation in many people
Why the cause matters
Understanding what caused the fissure helps direct the treatment:
- If diarrhoea caused it, managing the diarrhoea is more important than adding fibre
- If Crohn’s is involved, managing the underlying disease is essential
- If sphincter hypertonia is the primary issue, topical relaxants or surgery may be needed even without stool problems
- If medication is contributing, discussing alternatives with the prescribing clinician may help
A fissure that develops without an obvious cause, or that occurs in an unusual location, or that does not respond to standard treatment, warrants further investigation.