Hemorrhoids are lumps or masses of tissue in the anus, which contain enlarged blood vessels. Any increase in abdominal pressure may produce hemorrhoids. This may be from:
Repeated straining to have a bowel movement, especially in people who suffer from frequent constipation.
Repeated episodes of diarrhea.
Many patients have no apparent explanation for the formation of hemorrhoids, however.
Internal hemorrhoids. Internal hemorrhoids lie inside the anal canal, where they primarily cause the symptom of intermittent bleeding, usually with bowel movements, and sometimes mucous discharge. They are usually painless. Internal hemorrhoids also may protrude (prolapse) outside the anus, where they appear as small, grape-like masses. Usually the prolapsed hemorrhoid can be pushed back into the anus with a finger tip.
External hemorrhoids. These lie just outside the anal opening, where they primarily cause symptoms of swelling or bothersome protrusions, and sometimes discomfort. Swelling and discomfort may occur only intermittently. External hemorrhoids may also cause difficulties keeping the anal area clean after bowel movements. External hemorrhoids sometimes develop a blood clot inside of them ("thrombosis"), often after a period of diarrhea or constipation. In that case, it produces a sudden firm and painful swelling or lump around the rim of the anus.
Many patients have both internal and external hemorrhoids.
Hemorrhoids are a very common health problem. Hemorrhoids are more likely to develop in individuals who eat insufficient dietary fiber and don't get enough exercise, which can lead to repeated episodes of constipation and straining to have bowel movements.