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Hemorrhoids - Cause

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 hemorrhoids include:

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Understanding Hemorrhoids -- the Basics

Hemorrhoids are swollen blood vessels of the rectum. The hemorrhoidal veins are located in the lowest area of the rectum and the anus. Sometimes they swell so that the vein walls become stretched, thin, and irritated by passing bowel movements. Hemorrhoids are classified into two general categories: internal and external.   Internal hemorrhoids lie far enough inside the rectum that you can't see or feel them. They don't usually hurt because there are few pain-sensing nerves in the rectum...

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

Other things 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.

    This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

    WebMD Medical Reference from Healthwise

    Last Updated: March 16, 2012
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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