A hemorrhoid is an irritated clump of swollen veins in the anus and lower rectum, similar to varicose veins.  There are two main types of hemorrhoids: internal and external.  Internal hemorrhoids lie inside the rectum and rarely cause discomfort as they usually cannot be seen or felt.  However, straining or irritation when passing stool can damage a hemorrhoid’s surface and cause it to bleed.  External hemorrhoids are those under the skin around the anus.  When irritated, external hemorrhoids can itch or bleed.  Hemorrhoids are very common, affecting nearly three out of four adults on occasion.