Last updated:

Reviewed by:

Dr Bryony Henderson

, Lead GP at Livi

Medically reviewed

Threadworms are very common small worms that cause itching around the anus. Good hygiene can help break the cycle of infection, but having an infection doesn’t mean you have bad hygiene. Read more about threadworms and how they’re treated.

What are threadworms?

Threadworms, sometimes called pinworms, are small worms that can infect the digestive tract. While they’re unpleasant, they don’t cause serious problems and can be treated with medication. 

What do threadworms look like?

Threadworms are yellow-white, thin and 5-13 millimetres long. They look like small pieces of thread. You may be able to see them in your poo or on toilet roll. 

Threadworm eggs are small and usually impossible to see with the naked eye, but you may be able to make out tiny white specks. 

What are the symptoms of a threadworm infection?

Threadworms don’t always cause symptoms, but the most common symptom is itching, redness or pain around the anus. The itchiness may get worse at night when threadworms are most active, making it hard to sleep. 

In girls, the worms can also irritate the vulva (area around the vagina) or urethra. It’s common for a threadworm infection to occur at the same time as a urinary tract infection in young girls. 

Children with threadworms might be irritable, wake more than normal at night, lose their appetite or lose weight. Very young children might slide around on their bottoms. 

How common are threadworms?

Threadworms are common in children. In England, around half of children will get a threadworm infection at some point. Adults can also get threadworms. 

What causes threadworms?

Threadworms spread when their eggs are ingested. Threadworm eggs can survive for up to 2 weeks outside the body and stick to objects like clothing, sheets, furniture, towels, dust or pet fur. Touching something with eggs on it and then touching your mouth can lead to an infection.

How long do threadworms live?

The life cycle of a threadworm from egg to adult lasts over a month. The eggs can survive outside the body for several weeks. Once the eggs are ingested, it takes 3-4 weeks until the adult threadworms hatch in the gut. The threadworms will lay new eggs around the anus before they die. Children with threadworms can reinfect themselves if they touch their bottom and then put their fingers in their mouth.

The number of worms in an infection can range from just a few to several hundred of them. 

How is a threadworm infection diagnosed?

The symptoms of threadworm are often enough to diagnose them. If you can see small thread-like worms in your poo then this can be helpful. Sometimes, if the diagnosis is uncertain, a doctor may advise further investigation but this is usually not needed. 

How are threadworms treated?

The first step to treating threadworms is good hygiene to break their life cycle and prevent reinfection. Threadworms are very common and easily spread, so it’s hard to completely avoid them. Having threadworms doesn’t mean you have poor hygiene. Here are some steps you can take to stop the infection:

  • Wash hands often and scrub underneath fingernails, especially after using the toilet and before eating

  • Change underwear and pyjama trousers every day

  • Change bed linen, bath towels and hand towels regularly (every day during an active infection)

  • Wash toys regularly 

  • Do all laundry at a minimum of 60 degrees to kill any eggs

  • Change into fresh clothes as soon as you come home

  • Prevent dust by vacuuming and cleaning, especially in the bathroom and bedroom

  • Clean toilets and sinks daily

  • Bathe pets regularly

  • Keep fingernails short and avoid thumb-sucking or nail-biting

  • Have children wear gloves at night

A medication called mebendazole, which can be purchased from a pharmacy or on prescription, is the usual treatment given to kill threadworms if hygiene measures haven’t worked. It’s important to treat everyone in the household at the same time, even if they have no symptoms. A single dose is often enough, but you may need to repeat this after 2 weeks so that any remaining worms are killed. 

If you’re pregnant or breastfeeding, it’s important to speak to your doctor before taking any medication.

Children with threadworms don’t need to be kept home from school, but some schools have their own guidelines. Always tell the school staff if your child has threadworms.

Other possible explanations

Itching around the anus is not always caused by threadworms. There are also other types of worm infections, like roundworm, human whipworm or hookworm.

If you haven’t spotted any worms, things like eczema, fungal infections, anal fissures or piles can cause some similar symptoms.

When should I speak to a doctor?

If you or your child have threadworms that won’t go away or keep coming back, speak to a doctor. 

You should also see a doctor if you see slime or blood in poo, even if you don’t have other symptoms of a threadworm infection. 

How can Livi help?

Livi can help treat threadworms. A doctor will make an individual assessment based on your symptoms. You may then be given a prescription for treatment or referred for specialist care. 

Last updated:
Reviewed by:
Dr Bryony Henderson, Lead GP at Livi