What are pinworms?

Pinworms are tiny white worms, also known as Enterobius vermicularis, that live in the intestine. They are about the length of a staple. Pinworms are sometimes called threadworms because they look like a piece of white thread. 

Who is at risk?

Pinworm infection affects people of all ages. It occurs most often among school-aged children and preschoolers including those attending child care centres, people living in institutional settings, and household members and caregivers of persons with pinworm infection. Cats and dogs are not involved in the spread of pinworms.

How are pinworms spread?

Pinworm infection is spread by the transfer of infective pinworm eggs from the anus to someone’s mouth, either directly by hand or indirectly through contact with contaminated clothing, bedding, food, or other objects like toys. Pinworms are usually spread from child to child and from an infected child to their family members.

While an infected person sleeps, female pinworms leave the intestine through the anus and deposit their eggs on the surrounding skin. When the infected person scratches their anus, the pinworm eggs may get onto their hands and under their nails and can be spread to others.

Since pinworm eggs can survive outside of the body for up to two weeks, contact with objects contaminated with pinworm eggs can cause infection as well.

What are the symptoms?

Often there are no signs of infection. Itching and scratching around the anus is the most common symptom. In children, the itching may lead to disturbed sleep and irritability.


The best way to see if a child has pinworms is to examine the anus for worms two to three hours after the child is asleep. In addition, your healthcare provider may recommend a “tape test” which involves placing sticky tape on the skin around the anus. The pinworm eggs are picked up by the tape and are identified under a microscope.


Most pinworm infections are mild and can be treated with oral medication. After the initial dose, the medication is repeated two weeks later to decrease the risk of reinfection. If a member of a family has pinworms, treatment of all household members may be considered. Infected people should shower every morning and thoroughly wash the anal area as this removes a large amount of the eggs.

Preventing the spread of infection and reinfection

  • Thorough handwashing after using the toilet and before eating is the best way to prevent the spread of infection.

The best handwashing technique includes six steps:

  • Wet hands with warm running water
  • Apply liquid soap
  • Lather hands and scrub for 20 seconds
  • Rinse under running water
  • Dry your hands with paper towels
  • Use the towel to turn off the taps

Also best to:

  • Keep nails trimmed short and discourage nail biting and thumb-sucking.
  • Discourage scratching of the anal area.
  • Daily morning showering removes a large number of eggs. If showering is not possible such as with young children, the infected person should bathe while standing to avoid getting contaminated bathwater in the mouth.
  • Towels and washcloths should not be shared and should be washed using the hot water cycle and dried on the hot cycle in the dryer.
  • Underwear and pajamas should be changed and laundered daily. Bed sheets should be changed and laundered regularly especially after each treatment. The hot water cycle on the washing machine should be used to wash these items and a hot dryer should be used to dry them. Used bedding and clothing should be handled carefully since shaking can spread the eggs into the air.
  • Eggs are sensitive to light, so open bedroom curtains and blinds during the day.
  • Children with pinworms can continue to attend child care.
  • Ensure children’s nails have been cleaned and trimmed.

If you have any questions or concerns, please contact Health Line at 519-271-7600 or toll free at 1-877-271-7348 extension 267.


  • Canadian Paediatric Society, 2008. Well Beings A Guide to Health in Child Care, Third Edition.
  • Centers for Disease Control and Prevention, 2013. Parasites – Enterobiasis, also known as Pinworm Infection. Retrieved May 12th, 2015
  • Heymann, D.L., 2015. Control of Communicable Diseases Manual, 20th Edition. Washington, District of Columbia: American Public Health Association.

Developed by the Middlesex-London Health Unit and adapted with permission.

August 2016