A pinworm infection is called enterobiasis, and is caused by the parasitic worm Enterobiasis vermicularis. Other names for pinworm infection include seatworm infection and threadworm infection. Ascariasis is caused by a large intestinal roundworm. Trichinosis is caused by Trichinella spiralis, a roundworm that can be found in raw or undercooked pork or wild game. Strongyloidiasis is caused by another parasitic roundworm called Strongyloidiasis stercoralis.

Pinworms are tiny (one-half-inch), white, threadlike roundworms found primarily in the colon and rectum. They enter the body when pinworm eggs are swallowed. The eggs subsequently hatch in the small intestine. The larvae travel to the large intestine, where they attach themselves as parasites. Three to six weeks after the eggs are swallowed, the female worms move out of the body to lay eggs around the anus.

A female pinworm can lay thousands of eggs. The eggs are moist, making them able to stick to the fingers of children. If children with eggs on their fingers put those fingers in their mouth, the pinworm can enter the body. The eggs are laid around a child's anus. The eggs can then be scattered in the air from bed linen and clothing. The eggs can land and stick on doorknobs, furniture, tubs, faucets, toys, and food, the NIAID says. The eggs can survive for up to three weeks outside the human body.

The itching is caused by the female pinworm moving from the anus to lay her eggs. The female worm usually does this at night. The itching can occur around the anus or, in girls, the vagina. Sometimes the itching is so severe that the child's sleep may be disturbed, the NIAID says. Scratching the area may result in a bacterial infection.

Your health care provider may ask you to first look for pinworms. You can check for pinworms by using a flashlight to look at your child's anus several hours after he or she has gone to bed and then early in the morning. The worms resemble quarter-inch long white threads that move. You should check for the worms for two nights in a row. If you do not see a worm, your health care provider may give you cellophane tape attached to a tongue depressor to use in collecting the eggs. You gently press the tape to the area around the anus. The collection is usually done as soon as your child wakes in the morning, because bathing or having a bowel movement can remove the eggs. The tape is examined under a microscope to verify that eggs are present.

Children often are allowed to outgrow the infection without treatment, the NIAID says. When medication is prescribed, the entire family should take it. Drugs commonly used to treat pinworms include mebendazole and pyrantel pamoate. The medication is given in two doses, the second two weeks after the first. Your health care provider may prescribe an ointment or cream to relieve the itching.

The eggs are sensitive to sunlight, so experts recommend opening the blinds or curtains in the bedroom each day. Vacuuming or wet-mopping the bedroom each week can pick up any eggs that have scattered on the floor. Also, keep your child's fingernails trimmed short and discourage him or her from biting them or from sucking on a thumb. Even with the best hygiene, it's still possible for your child to become infected with pinworms if he or she swallows them. Just because your child has been in contact with a child who has pinworms doesn't mean your child will become infected. You should wait a month to check, however, because the eggs take three to four weeks to mature into adult pinworms.