Patient information from BMJ

Threadworm

Last published:Jul 09, 2024

Threadworms are tiny worms that can infect the lower gut. They are most common in children, and can cause an itchy bottom, around the anus. Threadworm infection can be annoying, but treatment is usually simple.

You can use our information to talk to your doctor and decide which treatments are best for you. 

What is threadworm infection?

Threadworms are tiny worms that live in the lower part of the gut, near the anus. They come out at night and lay eggs around the anus. This can cause intense itching. 

When you scratch – and this can happen in your sleep – the eggs get onto your hands. If you then swallow the eggs, the worms will hatch again in your gut. The eggs can also attach to anything you touch, and can survive there for up to 2 weeks. Eggs can spread to other people when they touch these surfaces and then touch their mouth.

Threadworm infection is unpleasant but it’s very common, especially among school-aged children and their carers. Threadworms are unlikely to cause any harm, except the discomfort from itching.

You may also hear threadworms called pinworms.

What are the symptoms?

Many people with threadworm infection don’t have any symptoms. If you do get symptoms you’re most likely to have a very itchy bottom, around the anus. This is especially worse at night and might make it hard to sleep. The area may be red and marked by scratching. Very rarely, itching may extend to the vulva in women and girls.

In children who are too young to say what’s wrong, you may notice that they are restless or can’t sleep at night.

Your doctor may be able to tell if you or your child has threadworms just by your description of the symptoms. But you may need to do a ‘tape test’. This means you put a small piece of transparent sticky tape over the skin around the anus. You do this first thing in the morning, for 3 days in a row. Your doctor will check this under a microscope for threadworm eggs. 

What treatments work?

The usual treatment is a type of medicine called an anthelmintic to kill the threadworms. 

The medicine comes as tablets or as a liquid. You need two doses, with two weeks between each dose. That’s because the medicine kills the threadworms but not their eggs. You need the second dose to kill any newly hatched worms. Most people who take two doses of this medicine get rid of the infection. 

Side effects are rare, but some people get stomach pain or diarrhoea.

There is not much research on whether this medicine is safe for pregnant women or for children under 2 years old. Your doctor will look at the risks and benefits to decide if this medicine is right for you or your child. If you’re pregnant, your doctor might suggest waiting until your third trimester (after 29 weeks) to start treatment.

Because threadworms spread easily between family members, your doctor may recommend that the whole family is treated, even if just one person has threadworm infection.

Things you can do yourself 

There are some simple hygiene measures you can take to reduce the chance of you or your child getting re-infected. 

• Wash your hands well and often, especially before eating or preparing food.

• Keep fingernails short and clean.

• Shower every morning.

• Use a shower rather than a bath, and avoid bathing more than one child in the same water.

• Discourage your child from sucking their thumb, biting their nails, or scratching around their bottom when they have an infection.

• If you or your child has threadworm infection, wash all your underwear and bed linen promptly. Avoid shaking the clothes and bed linen before you wash them, as this could spread the eggs around. 

What will happen to me or my child?

Threadworm infection is easy to get rid of with treatment. There are no long-term effects, but it’s quite common for people to get re-infected. Your child may get threadworms from other children, typically at school. The treatment is the same as for the first infection. Threadworm infection tends to become less common as children get older.