Threadworms, sometimes known as pinworms, are small, white, thread-like worms a few millimetres long, that live in the human gut.
Threadworms are more common in school or pre-school children than in adults, but can sometimes affect whole families, especially in overcrowded conditions.
Threadworm passes from person-to-person because of poor personal hygiene. The female worm lays eggs around the anus, which often leads to scratching. Eggs can then become stuck to fingertips or under the fingernails and be transferred to other people, to food, children's toys, kitchen utensils, or toothbrushes. Other people then come into contact with the eggs, and if they touch their mouths and swallow the eggs they become infected with threadworm.
You cannot catch threadworms from, or give threadworms to, your pets.
Although there is no way to completely prevent threadworm infection high standards of personal hygiene can reduce the risk. Children should be taught to wash their hands with soap and water regularly, particularly after going to the toilet and before eating.
Many people do not show any symptoms. But symptoms can include:
Itching around the anus (and in girls the vagina too), which becomes much worse at night
Disturbed sleep and irritability
Secondary skin infection due to bacteria entering scratches
Loss of appetite
When going to the toilet it looks as if the infected person is passing strings of white cotton thread. Threadworms can grow to become 2-13 millimetres long, living for up to six weeks in the host body. The eggs can survive for up to three weeks outside the body and can sometimes hatch on the skin and re-enter the bowel.
There are a variety of treatments available which you can get from your local pharmacy without a prescription. You should get advice from your GP if you are pregnant, breastfeeding or for infants under three months.
While using medication to treat threadworm you should follow strict personal hygiene measures to prevent re-infection. Drugs will kill the worms in the intestines but not the eggs laid outside the anus. Eggs can survive for up to three weeks outside the body, on underwear, bedding, in the dust, etc. When drug treatment is not wanted or not recommended, such as during pregnancy, breastfeeding, or in infants under three months, this method can be used to get rid of threadworms effectively.
All family members should be treated simultaneously, even if they do not show any symptoms.
For treatment to be successful, every member of the household should:
Wear close-fitting pants at night
As soon as they wake up each morning, have a bath or shower, washing especially around the anal region
Change and wash underwear, nightwear, and (if possible) bed linen and towels each day (avoid shaking them as this also spreads eggs). Avoid sharing towels or face flannels
Keep fingernails short
Wash hands and scrub under the nails first thing in the morning, after using the toilet or changing nappies, and before eating or preparing food
Put toothbrushes in a closed cupboard, and rinse them well before use
Avoid eating food in the bedroom (eggs can be shaken off bedclothes and survive in dust)
Discourage children from sucking their thumbs
Encourage children to wash their hands before eating and after visiting the toilet
In addition you should:
Disinfect bathroom surfaces daily
Vacuum carpets and damp dust surfaces daily, washing the cloth frequently in hot water
Make sure there is good ventilation and reduce humidity in the house.
Re-infection is common. If an infection is left untreated it could result in more serious problems such as insomnia, weight loss and bed-wetting.
Sometimes adult worms can spread to other organs, leading to complications such as inflammation of the vagina, pelvic inflammatory disease, urinary tract infection, and hepatitis but this is rare.
Intense scratching can damage the skin and it then becomes infected.
It is not necessary to stay away from work or school if you have threadworm. Teachers and care-givers should encourage good personal hygiene.
We issue guidelines for doctors and environmental health specialists and to schools on preventing the spread of infection from person to person.
More information about the Health Protection Agency and about threadworm is available on our website
If you have concerns about your health contact NHS Direct on 0845 4647 or visit their website www.nhsdirect.nhs.uk, or see your family doctor.
This factsheet can also be threadworms (PDF, 185 KB)
Last reviewed: 23 October 2008