Pinworms (threadworms)

About threadworms

Threadworms are the most common parasite infection of children in the UK. Threadworms are small, thin, white, thread-like worms that infect the human bowel. The adult female worm is 8 to 13mm long, and the male worm is 2 to 5mm long. Adult worms live for up to six weeks in your bowel. Threadworms are common in children but people of any age can be infected.

Symptoms of threadworms

Threadworms cause intense itching around your anus. In girls, vaginal itching can also occur. The itching is worse at night when the female worm is laying her eggs. This can make it difficult to sleep and skin infections can occur from itching the area and breaking the skin.

Causes of threadworms

Threadworms pass from person to person through poor hygiene. They live for up to six weeks in your bowel and then die. The female worms lay their eggs around your anus. This usually happens at night. As the female worm lays her eggs, she releases an itchy mucus which helps the eggs stick to your skin. When you scratch around your anus, the eggs get onto your fingers and under your nails. They can then rub off onto other surfaces that can come into contact with people's mouths, such as children's toys, toothbrushes or food utensils. If the eggs are swallowed, the cycle begins again. Threadworm eggs can survive for two to three weeks outside your body including on surfaces, bedding and towels before spreading to other people.

Threadworms are most common in children because they easily forget to wash their hands. Threadworms can’t be caught from pets, though the eggs can live in your pet’s fur if they’re passed onto your pet when you touch and stroke them.

Diagnosis of threadworms

Threadworms are difficult to see because they are so tiny. Sometimes you can see them in faeces – they look like small pieces of cotton thread. The eggs aren’t visible to the eye.

Your GP will usually be able to tell if you have threadworms from the symptoms of itching and disturbed sleep. Your GP may ask you to carry out the ‘sticky tape’ test. To do this you press some clear see-through tape onto the skin around your anus first thing in the morning, before you go to the toilet or bathe. Put the tape into a clean container and give it to your GP who will send it to a laboratory to be looked at under a microscope for eggs. Alternatively, your GP may take a sample from around your anus to collect some of the eggs with a moistened swab. Your GP will send it to a laboratory to be looked at under a microscope for eggs.

Treatment of threadworms

Threadworm infection can be treated with medicines and by following a strict hygiene routine.

Threadworms are often found in family groups, particularly those living in crowded conditions. So, if one person is infected then all household members, including adults and those without symptoms, should be treated. Threadworms don’t always cause symptoms so it’s important to treat the whole household in case a person doesn’t realise they’re infected.


Good hygiene can help clear up a threadworm infection and lower your chance of getting it again. Threadworm eggs can survive for two to three weeks outside your body, so even if you take medicines to kill the worms, you need to follow strict hygiene methods to stop any eggs from being swallowed.

  • Clear eggs from where they may be in your home – wash sleepwear, bedding, towels and toys. Don't shake the bedding or any clothing that may have eggs on it – carefully remove it and put into the washing machine.
  • Clean bathroom and kitchen surfaces with disinfectant, and vacuum and dust the whole house with a damp cloth.
  • Every morning have a bath or shower – carefully wash around your anus to get rid of eggs laid overnight.
  • Wash your hands and scrub under your nails first thing in the morning, after using the toilet or changing nappies, and before eating or preparing food.
  • Wear close-fitting underwear at night – this is so if you scratch in your sleep, you won’t touch the skin and also the eggs won't fall onto your bedding (also consider wearing cotton gloves at night to stop night-time scratching).
  • Keep your fingernails short and try not to bite your nails or suck your fingers. Discourage children from doing so.
  • Change your toothbrush, and rinse well before brushing your teeth and keep it in a closed cupboard.


You can buy medicines to treat threadworms over-the-counter from pharmacies, or your GP can prescribe them. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist or GP for advice.

The two medicines often used to treat threadworms are listed below.

  • Mebendazole. This is the treatment of choice for children over two years. A single dose kills the worms. You may be given a second dose after two weeks because the chances of getting it again are common.
  • Piperazine. This is suitable for children over three months. A second dose may be given after two weeks to prevent reinfection.

If you’re pregnant or are breastfeeding, consult your GP before taking any medicines. See our frequently asked questions for more information.

Prevention of threadworms

Good hygiene can help prevent threadworm infection. It’s important that you and your children wash your hands regularly, especially after going to the toilet and before meals.

The eggs can survive on bedding, clothes and other household surfaces for up to three weeks. Therefore, it's important that you regularly change your bedding, clothes and clean your bedroom, kitchen and bathroom surfaces with disinfectant.

My son has threadworms. Should I keep him off school?


No, your son doesn't need to stay off school.


Although threadworms are infectious, you don't need to stop your son going to school. By the time threadworm infection is noticed, it's likely to be too late to stop the infection spreading in the school, so there would be nothing to gain in keeping him at home.

Inform the school that your child has threadworms so that the teachers can make sure the children practice good hygiene, for example, wash their hands after going to the toilet and before having their lunch.

Likewise, should you develop threadworms, you can continue to work as normal but practice good personal hygiene such as hand washing.

I’m pregnant and I have threadworms, should I be treated?


No, you shouldn't take medicines to kill the worms when you’re pregnant.


Medicines used to treat threadworms aren’t licensed for use in pregnancy. Good hygiene can help clear up a threadworm infection and lower your chance of reinfection. Your doctor will recommend you practice good hygiene to clear the infection.

If the infection doesn't clear up with self-help measures, your doctor may prescribe mebendazole, but he or she will only consider this if you’re in the second or third trimester of pregnancy.

What happens if I don't treat the threadworms?


Threadworms cause intense itching around your anus at night. If left untreated, you may have difficulty in sleeping which could cause tiredness and irritability. Constant scratching may lead to inflammation, broken skin and infection.


Threadworms can cause intense itching around your anus and vagina. Constant scratching can cause your skin to become inflamed. If your skin is broken, this may lead to an infection.

It’s very rare for threadworms to live outside of your bowel. However, they have been known to spread into the vagina, womb (uterus), lining on the inside of the abdomen (tummy), liver, and even the lungs.

Reinfection is common if you don’t treat threadworms and it could become a persistent problem.