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What is thread worm (Enterobius)?

Enterobius, also known as threadworm, is an infection caused by small, white parasitic worms. These worms live in the large intestine and rectum of humans and adult worms can survive for five to six weeks. When an infected person sleeps, eggs are shed onto the skin around the anus where they can survive for two to three weeks.


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Enterobius is spread faeco-orally when threadworm eggs are swallowed. This can happen either by direct contact with a contaminated hand, or indirectly via contaminated items such as clothing, food, or sheets. Because of their small size, eggs sometimes can become airborne and ingested while breathing.

Infection can cause intense itching of the area around the anus as the female threadworm lays her eggs. It can also be asymptomatic. The ‘adhesive tape test’ helps to diagnose threadworm. This involves pressing transparent tape onto the skin around the anus. This should be done in the morning, before going to the toilet or washing and then the tape should be given to your doctor. This can then be examined under a microscope to look for threadworm eggs.

Mebendazole is the first-line treatment used to treat Enterobius which involves taking two doses, spread two weeks apart. If the treatment is used correctly and strict hygiene measures are followed, it should break the cycle.

Other members of the household should also be treated. Mebendazole should be avoided in the first trimester of pregnancy; treatment in pregnancy should be discussed with a medical practitioner.

Personal hygiene:

  • Keep finger nails 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 pants 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


  • “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.

The Hospital for Tropical Diseases,
2nd Floor, Mortimer Market Centre
Capper Street, London
020 3447 5968
Switchboard: 020 3456 7890


Have you travelled to a tropical country in the last 6-12 months and are you acutely unwell? You can be seen in our emergency walk-in clinic Monday to Friday 9am-4pm.

Our travel medicine service offers specialist travel advice including for individuals with complex health conditions. We offer this on a privately and via NHS referral basis. Please contact: or 020 3447 7999 for more information about our services.

If you need a large print, audio, braille, easy read or translated copy of this document, please contact us on 020 3456 7891 We will try our best to meet your needs.

Page last updated: 21 May 2024

Review due: 31 October 2025