What are the causes for Anal fissure?

Common causes of anal fissure include:

  • Passing large or hard stools
  • Constipation and straining during bowel movements
  • Chronic diarrhea
  • Inflammation of the anorectal area, caused by Crohn's disease or another inflammatory bowel disease
  • Childbirth

Less common causes of anal fissures include:

  • Anal cancer
  • HIV
  • Tuberculosis
  • Syphilis
  • Herpes

Source: http://www.mayoclinic.com