What is Fissure?
This is a cut (ulcer or Laceration) inside the anus. The usual cause is trauma to the anus because of a strained bowel movement, hard bowel movement, or high internal sphincter tone (the area that allows stool to pass stays tense, obstructing proper passage).

Symptoms
Severe tearing pain during a bowel movement

Throbbing pain in anus following a bowel movement

Blood on toilet paper or around the bowel movement

Cause
Constipation.
Constant irritation from stool in diapers of babies or constant wiping in all others.
Scratching due to infections (e.g., pinworm) or skin conditions (e.g., dry skin, Eczema).
Straining.
High internal sphincter tone (explained above).