Hemorrhoids (also known as "piles") are dilated or bulging veins of the rectum and anus, caused by increased pressure in the rectal veins. Fifty to seventy-five percent of all Americans develop hemorrhoids.

Hemorrhoids involve the blood vessels that line the anus. Pressure on the walls of the rectum weakens the muscles that support the hemorrhoidal vessels. They then become enlarged and lose their support and result in a sac-like protrusion inside the rectal canal (called internal hemorrhoids)...