Introduction 

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

Threadworms are a common type of worm infection in the UK, particularly in children under the age of 10.  

The worms are white and look like small pieces of thread. You may notice them around your child's bottom or in their poo.

They don't always cause symptoms, but people often experience itchiness around their bottom or vagina. It can be worse at night and 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 a prescription.

You only need to see your GP if you think you have threadworms and you're pregnant or breastfeeding, or if you think your child has threadworms and they're under two years old. In these circumstances, the recommended treatment is usually different.

How threadworms are 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 on to surfaces and clothes. If other people touch an infected surface, they can then transfer the eggs to their mouth.

Threadworm eggs can survive for up to two weeks before hatching. If the eggs hatch around the anus, the newborn 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 as there's a high risk of the infection spreading. This includes those who don't have any symptoms of an infection.

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

During treatment and for a few weeks afterwards, it's also important to follow strict hygiene measures to avoid spreading the threadworm eggs. This includes regularly vacuuming your house and thoroughly washing your bathroom and kitchen.

If you're 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's 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 reinfection and reduce the risk of the infection spreading to others.

Page last reviewed: 24/08/2015

Next review due: 24/08/2017