They don't usually hurt, because there are few pain-sensing nerves in the rectum. Bleeding may be the only sign of their presence. Sometimes internal hemorrhoids prolapse, or enlarge and protrude outside the anal sphincter. If so, you may be able to see or feel them as moist, pink pads of skin that are pinker than the surrounding area. Prolapsed hemorrhoids may hurt, because the anus is dense with pain-sensing nerves.
External hemorrhoids lie within the anus and are usually painful.
Blood clots sometimes form within prolapsed external hemorrhoids, causing an extremely painful condition called a thrombosis. If an external hemorrhoid becomes thrombosed, it can look rather frightening, turning purple or blue, and possibly bleeding. Despite their appearance, thrombosed hemorrhoids are usually not serious and will resolve themselves in about a week. If the pain is unbearable, your doctor can remove the thrombosis, which stops the pain, during an office visit. Hemorrhoids are the most common cause of anal bleeding and are rarely dangerous, but a definite diagnosis from your physician is a must.