Introduction 

Threadworms, also known as pinworms, are tiny parasitic worms that hatch eggs in and infect the large intestine of humans.

Threadworms are the most common type of worm infection in the UK, and they are particularly common in young children under the age of 10.  

Threadworms are white and look like small pieces of thread. You may notice them around your child's bottom or in your or your child's stools.

They don't always cause symptoms, but people often notice itchiness around their bottom or vagina. This can be worse at night and can sometimes disturb sleep.

Read more about the symptoms of threadworms.

When to see your GP

If you think you or your child may have threadworms, you can usually treat the infection yourself with medication available at pharmacies without prescription.

You only usually need to see your GP if you think you have threadworms and you are pregnant or breastfeeding, or if you think your child has threadworms and they are under two years old. This is because the treatment recommended in these circumstances is usually different to what is recommended for most people.

How are threadworms spread?

Threadworms lay their eggs around an infected person's anus (bottom), usually at night. Along with the eggs, the worm also secretes a mucus that causes itching.

If the eggs get stuck on the person’s fingertips when they scratch, they can be transferred to their mouth or onto surfaces and clothes. Other people who touch an infected surface can then transfer the eggs to their mouth.

Threadworm eggs can survive for up to three weeks before hatching. If the eggs hatch around the anus, the newly born worms can re-enter the bowel. Eggs that have been swallowed will hatch inside the intestine. After two weeks, the worms reach adult size and begin to reproduce, starting the cycle again.

Read more about what causes threadworms.

Treating threadworms

If you or your child has threadworms, everyone in your household will need to be treated because the risk of the infection spreading is high. This includes people without any symptoms of a threadworm infection.

For most people, treatment will involve a single dose of a medication called mebendazole to kill the worms. Another dose can be taken after two weeks, if necessary.

During treatment and for a few weeks afterwards, it is also important to follow strict hygiene measures to avoid spreading the threadworm eggs.

This involves things such as regularly vacuuming your house and thoroughly washing your bathroom and kitchen.

If you are pregnant or breastfeeding, hygiene measures are usually recommended without medication. This is also often the case for young children. 

Read more about treating threadworm infections.

Preventing threadworms

It is not always possible to prevent a threadworm infection, but you can significantly reduce your risk by always maintaining good hygiene and encouraging children to do the same.

Children should wash their hands regularly, particularly after going to the toilet and before mealtimes. Kitchen and bathroom surfaces should be kept clean.  

If your child is infected, encouraging them not to scratch the affected area around their anus or vagina will help prevent re-infection and reduce the risk of the infection spreading to other people.




Washing hands can help prevent a threadworm infection 

Should work or school be avoided?

A threadworm infection should be treated as soon as it's identified, but it is not necessary to stay off work or school.

However, it's important to inform your child's school or nursery so they can follow good hygiene practices to limit the spread of infection – such as cleaning toys and equipment, and encouraging children to wash their hands regularly.

Page last reviewed: 28/08/2013

Next review due: 28/08/2015