Pinworms are small nematode worms that are parasites on horses, rabbits, and other mammals. One type infests the human intestines and rectum. These pinworms are also called "seatworms" or "threadworms". They often occur in children between the ages of five and fourteen. Pinworms are not dangerous but can be irritating and lead to skin infections due to scratching.

The female pinworm lives in the intestine and crawls to the opening of the rectum at night to lay her eggs. The sticky coating that attaches the eggs to the skin is irritating and causes itching. The young pinworms are transferred to the hands when the child scratches.

Pinworm eggs are very small and can be breathed in from the air or can be swallowed when a child puts dirty hands in their mouth. Pinworms may also be spread from objects such as toys or clothing.

Pinworms are easily treated with a medication that is taken as a pill. Because pinworm eggs are so small, they can be spread easily from person to person in the same household. If one person in the home has pinworms, others may be infected.

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