Hemorrhoids are usually caused by increased pressure on the veins in the pelvic and rectal area. As pressure increases, blood pools in veins and causes them to swell. Eventually, the swollen veins stretch the surrounding tissue, and hemorrhoids develop.

Bowel habits that can cause increased pressure and lead to the development of hemorrhoids include:

• Rushing to complete a bowel movement. Hurrying can lead to excessive straining and increase pressure on rectal veins.
• Persistent diarrhea or constipation, which may cause straining and increase pressure on veins in the anal canal.

Other factors that can lead to the development of hemorrhoids include:

• Being overweight. Excess weight, especially in the abdomen and pelvis, may increase pressure on pelvic veins.
• Pregnancy and labor. Hormonal changes during pregnancy increase blood flow to the pelvis and relax supportive tissues while the growing fetus causes increased pressure on blood vessels. During labor, hemorrhoids may develop because of the intense pressure on the anal area while pushing to deliver the baby.
• Medical conditions. For example, long-term heart and liver disease may cause blood to pool in the abdomen and pelvic area, enlarging the veins.
• Tumors in the pelvic area. These occur very rarely.