Pinworm infection is caused by the small worm called Enterobius vermicularis. It is the most common worm infection in the United States and it most commonly affects school-age children.

The pinworm's only reservoir is humans, and the worms are transmitted from person to person by ingesting eggs (oral-fecal route), or through contact with contaminated bedding, food, or other items.

Upon ingestion of eggs, larvae eventually hatch in the small intestine and worms then mature in the colon. Female worms then migrate to the anal area, especially at night, and deposit their eggs. This may lead to itching and sometimes infection of the involved area.