You may first encounter pinworms if they’re going around your child’s school or day care center. Just hearing about them may make you feel queasy, but there’s no need for alarm Pinworms rarely cause serious problems, and they are easier to eliminate than lice.

Pinworms are a type of tiny roundworm (a nematode known as Enterobius vermicularis). They’re white, as thin as thread and about as long as a staple, according to the Centers for Disease Control and Prevention (CDC). What’s most unpleasant about them: Their favored habitat is the human colon and rectum, where they can cause excruciating itching.

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Children and pinworms

Pinworms are highly contagious, and they have an odd mode of transmission: They invade the body when someone swallows their eggs. The eggs then travel to the small intestine, where they hatch within two to six weeks. Female worms make their way to the large intestine and crawl out the rectum at night (causing intense itching) to lay thousands of microscopic eggs on nearby skin.

Here's why they are spread so easily among small children: When infected, kids often scratch their bottoms, get pinworm eggs under their fingernails, then touch something like a toy or school desk, according to the National Institute of Allergy and Infectious Diseases. Children who suck their thumbs or who neglect to wash their hands before eating are especially susceptible to pinworms, according to familydoctor.org, a website of the American Academy of Family Physicians.

Even if you are fastidiously clean, you may breathe in the tiny eggs through your mouth, according to the CDC.

Pinworms are the most common worm infection in the country and are especially common among young children and their families: One in five children gets pinworms at some point. In case you were wondering, though, pinworms never come from pets — they are spread only by people.

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Is it pinworms or just an itch?

The biggest tip-off is persistent anal itching, especially at night. Your child may have pinworms is if he is continually scratching (or complaining of itchiness) in the anal area, if he wets the bed or if he has trouble sleeping.

There are three simple ways to diagnose pinworms:

  • Touch the rectal area with transparent tape to trap eggs first thing in the morning, before bathing. You won’t be able to see the eggs because they are visible only under a microscope. Do this three mornings in a row and give the samples to your doctor. Your doctor can also give you a pinworm paddle, which is as sticky as tape, but easier to use.
  • If you’ve noticed a lot of scratching, your doctor can take a sample from your child’s fingernails and analyze it.
  • Inspect your child's rectal area with a flashlight two to three hours after he has fallen asleep and look for adult worms. (You may also want to use the transparent tape method to look for them.)

You can sometimes see tiny worms in the stool, but health agencies don’t recommend stool sampling since the worms are sparse there.

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Getting rid of pinworms

When one person in the family has pinworms, doctors often recommend treating everyone at the same time.

Your doctor may prescribe mebendazole to kill the worms. One dose is taken in tablet form (and again three weeks later if the infection has not cleared up), according to familydoctor.org. Your doctor may also recommend an over-the-counter medication called pyrantel, which is taken only once. (Let your doctor know if you are pregnant or breastfeeding before taking either of these medications and avoid pyrantel if you have liver disease).

The hardest part is making sure you don’t get any new worms. Since pinworm eggs can stay alive for up to three weeks on bedding and other items, the CDC and familydoctor.org recommend you take the following steps:

  • Wash all bedding, towels and clothes in hot water and dry in a hot dryer.
  • Keep everyone’s fingernails short and clean.
  • Scrub toilet seats, floors, toys, countertops and other surfaces.
  • Vacuum rugs and seat cushions.
  • Warm your hands with soap and warm water before handling food and after using the toilet or changing diapers.
  • Take a shower each morning to help remove pinworm eggs on the skin (avoid baths since the bath water could get contaminated).
  • Don’t bathe your children together if one child is infected.
  • Change your underclothes and bed linens daily each morning, but don’t shake the bedclothes because you may send the tiny eggs flying around the room.
  • Avoid scratching the anal region.

If you notice scratching and disturbed sleep every three to four weeks, see your doctor: You may have a re-infestation.

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Ana Manley-Black, J.D., is a former immigration attorney and a freelance health and medical writer whose stories have appeared in Healthday, Consumer Health Interactive, and other media.