Merck Manual

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Pinworm Infection

(Enterobiasis; Oxyuriasis)


Chelsea Marie

, PhD, University of Virginia;

William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Oct 2022
Topic Resources

Pinworm infection is caused by the intestinal roundworm Enterobius vermicularis and usually affects children, but adult members of their households and caregivers, institutionalized people, and those who have anal-oral contact with an infected partner during sex are also at risk.

  • 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 mebendazole, albendazole, or pyrantel pamoate given once at diagnosis and once 2 weeks later, usually cures the infection.

Pinworm infection is the most common roundworm infection in the United States, occurring in an estimated 20 to 42 million people. As many as a billion people worldwide from all socioeconomic classes are infected.

Most cases of pinworm occur in school-aged children, adults who care for children, or family members of an infected child.

Did You Know...

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

Transmission of pinworms

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.

Symptoms of Pinworm Infection

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.

Diagnosis of Pinworm Infection

  • Microscopic examination of transparent 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. This should be done 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.

Prevention of 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.

The following can help prevent the spread of pinworms:

  • Washing the hands with soap and warm water after using the toilet, after changing diapers, and before handling food (the most effective way)

  • Frequently washing clothing, bedding, and toys

  • Vacuuming the environment to try to eliminate eggs

  • If people are infected, showering every morning to help remove eggs on the skin

  • Avoiding oral-anal contact during sex

Treatment of Pinworm Infection

  • Mebendazole, albendazole, or pyrantel pamoate (drugs used to eliminate worms—anthelmintic drugs)

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

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

Drugs Mentioned In This Article

Generic Name Select Brand Names
Emverm, Vermox
Pin-X, Pronto Plus Pinworm, Reese's
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