Pinworms are small worms that infect the intestines.

Pinworms are the most common worm infection in the United States. They are most common in school-age children.

Pinworm eggs are spread directly from person to person. They can also be spread by touching bedding, food, or other items contaminated with the eggs.

Typically, children are infected by unknowingly touching pinworm eggs and putting their fingers in their mouths. The eggs are swallowed, and eventually hatch in the small intestine. The worms mature in the colon.

Female worms then move to the child's anal area, especially at night, and deposit more eggs. This may cause intense itching. The area may even become infected. When the child scratches the itching anal area, the eggs can get under the child's fingernails. These eggs can be transferred to other children, family members, and items in the house.