Intestinal worms can cause a rash or itching around the rectum or vulva. In some cases, you will pass a worm in your stool during a bowel movement. Some people may have intestinal worms for years without experiencing any symptoms. Sometimes the worms are visible in the anal area, underwear, or in the toilet. In stools, the worms look like small pieces of white cotton thread. Because of their size and white color, pinworms are difficult to see. The male worm is rarely seen because it remains inside the intestine. For most people, treatment will involve taking a single dose of a medication called mebendazole to kill the worms. If necessary, another dose can be taken after 2 weeks. During treatment and for a few weeks afterwards, it’s also important to follow strict hygiene measures to avoid spreading the threadworm egg.