Anal fissures are usually caused by small tears in the anal lining from mechanical strain (like hard stools or frequent diarrhea), sometimes worsened by underlying conditions that affect blood flow or inflammation in the area.

What is an anal fissure?

An anal fissure is a small tear in the thin skin (anoderm) lining the anal canal, typically just inside the opening. This tear exposes sensitive tissue and nerves, so it can cause sharp pain and bright red bleeding during or after a bowel movement.

Main direct causes

Most fissures start with local trauma to the anal lining.

Common triggers include:

  • Passing large, hard, or dry stools (chronic constipation).
  • Straining on the toilet for a long time.
  • Frequent or explosive diarrhea that repeatedly irritates the area.
  • Vaginal childbirth, especially prolonged or difficult labor.
  • Anal intercourse or inserting objects into the anus without adequate lubrication and relaxation.
  • Previous anorectal surgery or procedures that make the tissue more fragile.

In many people, a single episode of “bad constipation” or a bout of severe diarrhea is the clear starting event.

Why some fissures become chronic

Not all fissures heal quickly; some turn into a stubborn, chronic problem.

Key factors that keep a fissure from healing include:

  • High anal sphincter tone : The internal anal sphincter can go into spasm after the tear, increasing pressure and pain. This reduces blood flow, slowing healing.
  • A “vicious cycle”: Pain → more sphincter spasm → more tearing with each bowel movement → more pain.
  • Poor blood supply in that region, which is naturally a bit less vascular and even more so in older adults.
  • Repeated trauma from ongoing constipation, diarrhea, or continued anal penetration.

In chronic fissures, doctors may see features like a visible ulcer, a small skin tag (sentinel pile), or thickened edges of the tear.

Underlying medical conditions

Sometimes fissures are a sign of deeper systemic or inflammatory issues rather than just constipation.

Conditions that can predispose to anal fissures include:

  • Inflammatory bowel disease (Crohn’s disease, ulcerative colitis) causing chronic inflammation around the anus.
  • Sexually transmitted infections (e.g., syphilis, herpes, HIV-associated lesions, HPV) that damage the tissue.
  • Other infections or conditions like tuberculosis, leukemia, anal cancer, or AIDS-related lesions when fissures appear in unusual locations.
  • Disorders that reduce local blood flow, especially in older adults.

When fissures are off the typical midline or multiple, clinicians are more suspicious of these underlying causes.

Risk factors & when to worry

Certain people are more likely to develop fissures, or to have them recur.

Notable risk factors:

  • Age 15–40 and young children (higher incidence).
  • Chronic constipation or chronic diarrhea.
  • Pregnancy and postpartum period.
  • Low-fiber diet, dehydration, and sedentary lifestyle.
  • History of anorectal surgery or disease.

See a healthcare professional promptly if:

  1. Pain or bleeding persists longer than a few weeks.
  2. The pain is very severe, or you avoid bowel movements out of fear.
  3. There are multiple fissures, lateral fissures, or other symptoms (weight loss, fever, mucus, significant changes in bowel habits).

Information gathered from public forums or data available on the internet and portrayed here.