How does a pinworm infection develop?

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How does a pinworm infection develop?
(Pinworm Eggs Under a Microscope - Image in Public Domain, Courtesy of the CDC)

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How Does a Person Get Pinworms?

Pinworms are small, white thread-size worms that live in the intestines of humans. The 1/4-inch long parasites are relatively harmless yet can cause annoying itching. They are contracted orally when pinworm eggs are inadvertently swallowed. Pinworm eggs are too small to see with the naked eye. After pinworm eggs are swallowed, they move to the small intestine where they hatch and develop into larvae. Once they reach maturity, in 2 to 6 weeks, they move to the large intestine to live. Adult pinworms mate in the large intestine. The adult female pinworm, travels through the rectum and lays her eggs on the outside of the person's anus. After laying her eggs, she travels back into the large intestine. The eggs stick to the person's anus until they hatch. Once they hatch, they enter through the person's anus to go live in the intestines.

How Does a Person Swallow Pin Worm Eggs?

A person swallows pinworm eggs after touching an object that has the eggs on it. The eggs get on the hands and when the person puts his hands in his mouth, the eggs get into his mouth and he swallows them. Pinworm eggs can get on food after a person with pinworm eggs on his hands touches the food. The eggs can live outside of the body for approximately 2 weeks. A person can contract pinworms from participating in oral sex with a person infected with pinworms. Eggs that are on a person's anus may get into the mouth of the sex partner during oral sex. Rarely, pinworm eggs are found in the air, where they can enter the mouth through inhalation.

Pinworm Reinfection

A person infected with pinworms can reinfect herself, by scratching her anus and getting pinworm eggs under her fingernails. Pinworms under the fingernails can be transferred to food or objects. Pinworms that are under the fingernails can also be transferred into the mouth when the person puts her fingers in her mouth.

Symptoms of Pinworms

People who are infected with pinworms may not experience any symptoms at all. Some people do experience itching in the anus area. Females may also experiencing itching in the vaginal area. Sometimes people spot adult female pinworms who are laying eggs on the anus. Symptoms tend to be worse at night when pinworms are most active.

Who Gets Pinworm Infections?

Anyone can get a pinworm infection. Pinworm infections are most common in school-age children because they spend school days in an enclosed area around many children, some of who most likely have a pinworm infection. Pinworm infections are very common.


A doctor prescribes a prescription medicine that kills the pinworms. Two doses are taken, 2 weeks apart. Usually every member of the household is treated as a precaution, because pinworm infections are so contagious. All clothing and sheets should be washed to kill any pinworm eggs.

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