What are threadworms?

Threadworms (pinworms) are the most common parasitic worms found in temperate countries and usually affect children.

The worms can be spread by children sucking objects or eating food which is contaminated by threadworm eggs. Threadworms are parasites which live in the intestines, but at night the females come out of the rectum to lay their eggs on the skin around the anus. These eggs can cause itching and sometimes inflammation as a result of the person scratching the area constantly. Eggs on the fingers or under the nails can then be transferred to the mouth of the sufferer or other persons, maintaining or spreading the infection. The eggs may also survive in dust for up to two weeks and may be passed on if the dust is inhaled.

If a child has threadworms it is usual for the whole family to be treated as other members may also be infested even if they do not have any symptoms.


The tiny worms, like threads of cotton, may be seen moving on faeces. You may be asked to apply a piece of clear adhesive tape to the skin near the anus. Threadworm eggs will stick to it, and can be seen under the microscope.

What treatment is available?

Threadworms are usually treated with mebendazole. Mebendazole may be prescribed as Vermox® or bought over the counter from a pharmacist as Ovex®. With these treatments, patients are often advised to repeat the dose after 14 days to help prevent re-infection.

Self-help measures:

  • Ensure you always wash your hands after going to the toilet and before meals
  • Shower daily to remove any eggs from the anal area, change underwear daily and bedding regularly
  • Keep fingernails short, ideally children should wear cotton gloves to bed
  • Keep your house as dust-free as possible
  • Treat the whole family on the same day to avoid reinfection

Fact sheet provided by MIMS

Date last reviewed: February 2008

MIMS Clinics

Prescribing news and resources for key therapeutic areas, collated by the MIMS editors.

Register or Subscribe to MIMS

GPs can get MIMS print & online and GPonline for free when they register online – take 2 minutes, and make sure you get your free MIMS access! If you're not a GP, you can subscribe to MIMS for full access.

Register or subscribe

MIMS bulletins

News and updates straight to your inbox.

Prescribing Update: Fortnightly news bulletin
Urgent prescribing updates
Spotlight: Disease-themed monthly round-up

Sign me up

MIMS Dermatology

Read the latest issue online exclusively on MIMS Learning.

Read MIMS Dermatology

Mobile apps

MIMS: access the full drug database and quick-reference tables on the go

MIMS Diagnosis and Management: concise information on signs and symptoms, investigations and diseases

Promo Image

Clinical calculators

Handy calculators and conversions for primary care.