Hemorrhoids form when increased pressure on the pelvic
veins causes veins in the anal canal to swell and gradually stretch out of
shape. Pressure increases can be caused by rushing to complete a bowel
movement, persistent diarrhea or constipation, or other factors including being
overweight or pregnant.
Persistent pressure also weakens tissues
that support the veins in the anal canal. If those tissues become so weak that
they can no longer hold the veins in place, the swollen veins and tissues bulge
into the anal canal (internal hemorrhoids) or under the skin surrounding the
anal opening (external hemorrhoids).
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...
For some people, hemorrhoids
may cause a little discomfort for a limited time. Other people have recurrent
bouts of discomfort when hemorrhoids flare up. Some people struggle with
hemorrhoid pain, discomfort, and itching much of their lives. The degree and
duration of discomfort depend on where the hemorrhoids are.
Hemorrhoids frequently develop during pregnancy because of extra pressure on
veins (from the enlarged uterus).
During labor, hemorrhoids may
start or get worse because of the intense straining and pressure on the anal
area while pushing to deliver the baby. For more information, see the topic
Because external hemorrhoids
may not cause any symptoms, you may not be aware that you have
When a vein within an external hemorrhoid gets irritated, blood may clot under the skin, forming a hard, bluish lump. This is
known as a thrombosed, or clotted, hemorrhoid. Thrombosed hemorrhoids can be
Small internal hemorrhoids
may not grow larger if bowel habits or other factors change to lower pressure
on the veins in the bowel.
Large internal hemorrhoids may bulge
from the anus. After bowel movements, you may have to push them back through
the anus. At worst, large internal hemorrhoids stick out all the time.
In rare cases, hemorrhoids may bulge through the anus and swell. Muscles
that control the opening and closing of the anus may cut off a hemorrhoid's
blood supply (strangulated hemorrhoid). This may cause the hemorrhoid tissues
to die. If this happens, you will feel severe rectal pain and may see blood and
pus at the anus. You will need urgent surgery to prevent further complications,
such as death of the affected tissue and infection.
In this article
This information is produced and provided by the National
Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National
Institute via the Internet web site at http://
.gov or call 1-800-4-CANCER.
WebMD Medical Reference from Healthwise
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