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 5/15/2017
Updated by: Debra G. Wechter, MD, FACS, general surgery practice specializing in breast cancer, Virginia Mason Medical Center, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.