What Happens

The time it takes from when the eggs first enter your body to the time that an adult female pinworm lays new eggs is about one month. The eggs of pinworms get into the body through the mouth and develop into worms in the lower digestive system. They begin growing in the small intestine and move into the large intestine, where they become adult worms. The worms live by eating nutrients found in your digested food.

Female pinworms crawl out of the body and lay their eggs during the night on the skin around the anus. The female worm's wiggling motion when laying eggs is believed to irritate the skin and cause itching. The eggs have a damp, sticky covering, so when children scratch the skin around the anus, eggs stick to their fingers and get stuck under their fingernails. The eggs can then be transferred into their mouths or onto objects such as faucets and food. The eggs can also stick to clothing, bedding, and furniture. The eggs can live 2 to 3 weeks outside the body.

How pinworms are spread

Pinworms are spread when someone with pinworms scratches around the anus, gets eggs on his or her hands (or under the fingernails), and touches another person or an object. Infection can occur when:

• An uninfected person puts a hand in his or her mouth after being touched by an infected person.
• An uninfected person touches a pet or an object (such as bedding, clothes, dishes, or toys) that carries pinworm eggs and then puts a hand in his or her mouth.
• Bedding or clothes of a person who has pinworms are fanned in the air. Eggs can float through the air and be swallowed by other people.

A person with pinworms can be reinfected by any of the means listed above or when eggs hatch on the skin around the anus and the young worms (larvae) crawl back into the body.

Pinworm infection is contagious as long as living pinworm eggs are spread to and swallowed by someone. Because the medicine to treat pinworm infection kills adult worms but not pinworm eggs, a person who has received one treatment for pinworms can still spread the infection. This is why it is important to wash your hands often when you know that someone is infected. A second treatment with medicine is needed about 2 weeks after the initial treatment to kill any worms that have hatched during that time.

Complications

Complications from pinworms are rare. The most frequent complications are bacterial infection around the anus or of the skin in the genital area. This is usually because of skin irritation or scratches from itching in these areas.