Hemorrhoids are swollen veins in the rectal area that can form internally or externally from increased pressure in the veins of the pelvis or rectum. They can be caused by straining during bowel movements, remaining on the toilet a long time to move stool, and pregnancy. The symptoms most commonly are bleeding during bowel movements, rectal pain, and itching. External hemorrhoids can get irritated and clot, causing a painful, hardened lump, called a thrombosed hemorrhoid. Rectal bleeding can be a sign of a more serious problem, so it is important to see a doctor when it occurs.