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Pinworm Infection


By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

Pinworm infection is caused by the intestinal roundworm Enterobius vermicularis and usually affects children.

  • People acquire the infection when they swallow eggs of the roundworm.

  • The infection may cause itching around the anus.

  • The infection can be diagnosed by finding the eggs or sometimes the adult pinworm around the anus.

  • An antiparasitic drug such as albendazole, given once at diagnosis and once 2 weeks later, usually cures the infection.

Pinworm infection is the most common roundworm infection in children in the United States.

Did You Know...

  • Pinworm infection is the most common roundworm infection in children in the United States.

Transmission of pinworm

Infection occurs after pinworm eggs (ova) are swallowed. The larvae in the eggs hatch in the small intestine, then move to the large intestine. There, the larvae mature within 2 to 6 weeks, and the adult worms mate. After the eggs develop, the adult female worm moves to the rectum and exits through the anus to lay eggs. The eggs are deposited in a sticky, gelatinous substance that sticks to the skin around the anus. From there, eggs can be transferred to fingernails, clothing, bedding, toys, or food. Eggs can survive outside the body up to 3 weeks at normal room temperature.

Eggs are often introduced into the mouth from fingers or from contaminated food. Children may reinfect themselves by transferring eggs from the area around their anus to their mouth. Children who suck their thumbs are at increased risk of infection, as are adults who live with children or who practice oral-anal sex.


Many children who carry pinworms have no symptoms. However, in some, the area around the anus itches because the eggs and the sticky substance around them irritate the skin. With scratching, the skin can become raw and infected with bacteria. In girls, pinworms may cause vaginal itching and irritation.


  • Examination of tape that has been patted around the anus to collect eggs

  • Observation of adult worms around the anus

The diagnosis of pinworm infection is made by finding the eggs or, less commonly, adult pinworms around the anus. Eggs can be obtained by patting the skinfolds around the anus with the sticky side of a strip of transparent tape. Eggs should be obtained in the early morning before the child defecates or wipes the area. The tape can be taken to the doctor for microscopic examination. Doctors may ask parents or caregivers to repeat this procedure several days in a row to make sure that they obtain eggs, if present.

The best way to search for adult pinworms is to examine the child’s anus about 1 to 2 hours after the child has been put to bed for the night. The worms are white and hair-thin, but they wiggle and are visible to the naked eye.


  • Mebendazole or albendazole (drugs used to eliminate worms—antihelminthic drugs)

A single dose of mebendazole or albendazole, repeated after 2 weeks, usually cures pinworm infection.

Despite successful drug treatment of pinworm infection, reintroduction of infection is common, partly because eggs can survive outside the body for 3 weeks. Thus, some doctors recommend treating the entire family. Clothing, bedding, and toys should be washed frequently, and the environment should be vacuumed to try to eliminate eggs.

Anti-itching creams or ointments, such as carbolated petrolatum, applied directly to the area around the anus may relieve symptoms.

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