Hemorrhoids are varicose veins of the rectum. The hemorrhoidal veins are sited in the lowest area of the rectum and the anus. Sometimes they swell, so that the vein walls become stretched, slim, and irritated b passing bowel movements. When these veins bleed, itch, or hurt, they are known as hemorrhoids, or piles. Hemorrhoids are divided in two general categories: internal and external.
Veins in the rectum and anus are under considerable pressure whenever a stool is passed. Pushing or straining may cause veins in the rectal wall to lump, creating clusters of swollen, or dilated, veins called hemorrhoids. Internal hemorrhoids can form anywhere inside the anal canal, while external hemorrhoids are visible, or just below, the opening of the anus.