Pinworms are parasites about the length of a staple that live in the rectum. They are the most common worm infection in the United States. Pinworms get inside the body when you swallow their eggs. While you sleep, the female pinworms leave the intestines through the anus and deposit eggs on nearby skin. This can cause intense anal itching. Complications from pinworms are rare.

People get pinworm infections from one another. School-age children and preschoolers are most likely to get pinworms. You do not get them from pets. If you have a mild case, you may not need treatment. If you do need treatment, you and members of your family usually take medicine, since pinworms are spread so easily.