The most common causes of hemorrhoids are straining at bowel movements, prolonged sitting and pregnancy. Internal hemorrhoids occur above the anal sphincter, and external hemorrhoids occur below, outside the anal canal.
Review Date 4/13/2020
Updated by: Michael M. Phillips, MD, Clinical Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.