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.
Update Date 4/5/2015
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, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.