Pinworms are a type of parasite that lives in the digestive system of humans. Adult pinworms look like small, white threads that are no more than 13 mm (0.5 in.) long. You need a microscope to see the eggs.

They are common throughout the world, especially in school-age children. Pinworms spread easily in families, daycare centres, schools, camps, and other places where groups of people live. If one person in your family has pinworms, others probably do too. Pinworm infections can happen to anyone. They are not related to being unclean.

Most people get pinworms by swallowing the worms’ eggs. This happens when someone with pinworms scratches around the anus, gets eggs on his or her hands (or under the fingernails), and touches you or a surface that you later touch. When eggs get on your hands or food and then you eat, the eggs go into your mouth. And they move into your stomach and then to your rectal area.

The eggs turn into worms in about a month. A pinworm crawls out of the body during the night and lays eggs on the skin around the anus. The wiggling motion when the worm lays eggs may irritate the skin and cause itching.

Pinworms don’t usually cause serious health problems, and they do not carry disease. The most common sign of pinworms is itching around the anus. Many people with pinworm infections have no symptoms and may never be aware of the infection. In rare cases, itching becomes severe and may cause restless sleep, loss of appetite, and anxiety. It is possible to get a skin infection from scratching around the anus.

The incubation period — the time from first contact with eggs until symptoms appear — is usually 1 to 2 months or longer. There is no way to find a pinworm infection until symptoms appear.

Your doctor can find out if you have a pinworm infection by checking the skin around your anus. He or she may ask you to collect a sample from around the anus by using a piece of clear, sticky tape. This piece of tape will be put under a microscope to look for pinworm eggs.

You can treat pinworm infections with over-the-counter and prescription medicines. These medicines can help keep you from getting infected again and from spreading pinworms to other people.

To limit the chances of getting pinworms or of spreading them to others:

  • Wash your hands carefully and often.
  • Avoid scratching around your anus.
  • Keep your fingernails short.
  • Wash clothes and bedding regularly.
  • Bathe and change your underwear every day.

If family members get pinworms again, all family members will need to take medicine to kill pinworms.