Hemorrhoids may have a number of predisposing causes, but in most cases, increased pressure in the abdomen plays a key role. Some of the most common underlying factors for developing hemorrhoids include straining during bowel movements, pregnancy, repeated lifting of heavy objects, prolonged sitting or standing, and being overweight. The excessive pressure can cause the small veins around the anus and rectum to stretch. As the veins lose their elasticity, they become distended with blood and more likely to thrombose and become more fragile. This may result in bleeding, which is often the first indication of hemorrhoids.

Some people can have a single episode of symptoms from hemorrhoids, and others are plagued by ongoing symptoms all of their lives. It is common for a woman to experience hemorrhoids during pregnancy and/or delivery, and then have a resolution shortly after birth, never to have a problem again.