Hemorrhoids are usually caused by increased pressure on the veins in the pelvic and rectal area. As pressure increases, blood pools in the veins and causes them to swell. Eventually, the swollen veins stretch the surrounding tissue, and hemorrhoids develop.
Several factors may cause this swelling, including:
Another cause of hemorrhoids is the weakening of the connective tissue in the rectum and anus that occurs with age.
Pregnancy can cause hemorrhoids by increasing pressure in the abdomen, which may enlarge the veins in the lower rectum and anus. For most women, hemorrhoids caused by pregnancy disappear after childbirth.