What is threadworm (Enterobius)?
Enterobius, also known as threadworm and pinworm, is an infection caused by small, white parasitic worms. It is the commonest parasitic worm in the UK and is most common in children under 11 and their families. It is easily transmitted between people so can cause outbreaks in families or schools.
People become infected with threadworm by accidentally swallowing a worm egg. The adult worms live in the large intestine and deposit eggs on the skin around the anus. The eggs cause inflammation which can cause intense itching. The eggs are very sticky, so can get onto clothing or sheets or contaminate your hands when you scratch. They can survive and remain infectious in the environment for two to three weeks. When an egg is swallowed, it takes about 3–6 weeks for the worm to mature to cause symptoms and lay eggs.
Infection can cause intense itching or a wriggling sensation in the area around the anus. This is usually worse at night. Sometimes it can also cause inflammation in the skin around the vagina and it may contribute to bed wetting and poor sleep in children. 50% of people with threadworm have no symptoms at all.
Threadworm cannot spread or infect other parts of your body such as your nose or eyes.
Often people treat threadworm without a confirmed diagnosis. However, if you or your family members, are getting recurrent or difficult to treat infection it is important that we confirm the diagnosis and exclude other causes of your symptoms.
Threadworm can be diagnosed by either seeing the worm or the eggs in the laboratory. If you see a worm, this can be submitted to the clinic in an empty sterile container for confirmation in the laboratory. Alternatively, the laboratory can look for eggs either on a slide or swab. The eggs are not visible by eye as they are very small.
The ‘adhesive tape test’ involves pressing transparent tape onto the skin around the anus and placing it on a clear slide. The swab test involves wiping a damp swab around the anus. The tests should be done in the morning, before going to the toilet or washing and then submitted to the clinic. Because eggs aren’t always present around the anus, we usually need to examine at least three samples taken on consecutive mornings.
Mebendazole is the first-line treatment used to treat threadworm and is available from your local pharmacy. The standard dose is one tablet on day 1, then another tablet two weeks later on day 14. Sometimes an additional dose is needed on day 28. Strict hygiene measures are also required. Because threadworm is very infectious and some people have no symptoms, all household members and sexual contacts should be treated at the same time even if they do not have any symptoms.
Some families get frequent episodes of threadworm and may need to be seen in our family clinic for further support or longer courses of treatment.
Mebendazole should be avoided in the first trimester of pregnancy; treatment in pregnancy should be discussed with a medical practitioner.
Personal hygiene:
- Keep fingernails short and clean underneath with a brush once a day/after defaecation. Avoid biting nails and scratching the perianal area.
- Wash/shower every morning to remove eggs from the perianal skin.
- Always wash hands well with soap and warm water after using the bathroom and before eating.
- Wear a onesie or tightfitting nightwear in bed – and change daily, washing at 40ºC or above. Consider wearing cotton gloves at night to avoid scratching.
- Do not share towels.
- Do not co-bathe.
Environmental:
- “Hot wash” (>60º) sheets initially and then at least weekly – in the morning, do not shake before washing.
- Wearing a face mask and gloves strip the bed and vacuum the mattress and the whole bedroom once a week which again will reduce egg burden and thus minimise the chance of re-infection.
- Regularly change bath towels.
- Regular cleaning of surfaces.
- Fluffy toys in bed should be hot washed.
British Association of Dermatologists leaflet on pruritus ani.
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Email: uclh.
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Page last updated: 23 April 2026
Review due: 31 March 2028