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Threadworms infect the gut and lay eggs around the anus which causes itchiness. Threadworms are common but are not usually serious. Treatment usually includes medication plus hygiene measures.

Medication kills the worms but not their eggs, which can survive for two weeks. Therefore, strict hygiene measures are advised for two weeks after taking medication, in order to prevent the swallowing of eggs which may cause a new infection.

All household members should be treated at the same time, including those without symptoms.

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What do threadworms look like?

What are threadworms?

Threadworms are small, thin, white, thread-like worms between 2 mm and 13 mm long. They infect human guts (intestines). Worms in children are very common but anyone of any age can be affected. A threadworm is called a pinworm in some countries.

The image shows two female threadworms next to a ruler. The markings on the ruler are 1 mm apart so these threadworms are about half a centimetre long.



How do you get threadworms in the first place?

Typically someone with threadworms (often a child), touches their bottom (either when they are cleaning themselves after going to the toilet or when they are scratching) and one or more of the tiny eggs gets caught under their fingernail. If they do not wash their hands thoroughly at the time, this egg can get transferred to a surface such as a door handle. When someone else touches that surface the egg then transfers to their hand. When that next person puts their hands in their mouth (for example when eating or biting their fingernails), the egg is swallowed and moves into their digestive tract; the worms then hatch from the eggs and the cycle starts again.

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The life cycle of threadworms

Threadworms live for about 5-6 weeks in the gut and then die.

Before they die, the female worms lay tiny eggs around the back passage (anus). This tends to occur at night.

The eggs are too small to see without a microscope but cause itching around the anus due to mucus that surrounds the eggs being irritating to the skin. This area around the anus is then scratched to relieve the itching, often during sleep. These eggs get on to fingers and under fingernails and can then be swallowed as described above.

Any eggs that are swallowed then hatch and grow into adult worms in the gut. So a cycle of threadworm infection can go on and on. Very rarely, threadworms in the nose have been discovered.

The number of threadworms in the gut during an infestation varies from person to person.

How long do threadworm eggs live for?

Threadworm eggs can survive for up to two weeks outside the body. They fall off the skin around the anus and can fall on to bedding, clothes, etc. They can then get wafted in the air as clothes and bedding etc is changed.

Some eggs may settle on food or toothbrushes. So, children may swallow some eggs by playing with other children who have eggs on their fingers, or from food or toothbrushes that have been contaminated with threadworm eggs.

Threadworm symptoms

Common symptoms include:

  • Spotting worms in the poo (faeces) or near to the back passage (anus). They look like thin, white, cotton threads.

  • Severe itching around the anus.

  • Waking up during the night as a result of the itching.

  • Young girls in particular also often complain of severe itching around the vulva and vagina, usually in the night or soon after going to bed. They may feel that they need to pass urine urgently and keep going to the toilet even though they have an empty bladder. Sometimes this can get confused with vulvovaginitis or thrush.

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Are threadworms dangerous?

Not usually. Often, the worst thing about them is the itch and discomfort around the back passage (anus) which can wake people from sleep. Scratching may make the anus sore.

Large numbers of threadworms may possibly cause mild tummy (abdominal) pains and make a child irritable. In girls, threadworms can wander forwards and lay their eggs in the vagina or urethra (the tube through which you pass urine).

Rarely, threadworms can cause other problems such as loss of appetite and weight loss.

Threadworms treatment

All household members, including adults and those without symptoms, should be treated. This is because many people with threadworm infection do not have any symptoms. However, they will still pass out eggs which can then infect other people.

If one member of a household is infected, it is common for others also to be infected. So, everyone needs treatment.

The common treatments are:

  • To take a threadworm medicine to kill the worms in the gut; and

  • Hygiene measures to clear eggs which may be around the back passage (anus) or in the home.

Note: for babies under the age of 3 months, only hygiene measures are possible, as no medicine is licensed for this age group.

How to get rid of threadworms naturally

Medication will kill the worms in the gut but not the eggs that have been laid around the anus. .

Hygiene measures aim to clear any eggs from the body and the home, and to prevent any eggs from being swallowed. This will then break the cycle of re-infection.

  • First, as a one off, it is important to try to clear eggs from where they may be in the home. This means:

    • Washing sleepwear, bed linen, towels and cuddly toys.

    • Vacuuming and damp-dusting the home.

    • Thoroughly cleaning the bathroom by damp-dusting surfaces, washing the cloth frequently in hot water.

  • Then, every member of the household should do the following for two weeks:

    • Wear close-fitting underpants or knickers in bed, and change every morning.

    • Every morning have a bath, or wash around the anus straight away, to get rid of any eggs laid overnight.

    • Ideally, change and wash nightwear each day.

It is often not the home which is a main source of threadworm eggs. Children may come into contact with eggs in schools or nurseries, particularly in the toilets if they are not cleaned properly. This is why a child may have recurring threadworms, even if the home and personal hygiene are of a very high standard.


Mebendazole is the usual treatment for people aged over 2 years. If children are over 6 months but under 2 years, they can still take the medicine but it is unlicensed. Threadworm liquid or chewable tablet medicine is available for children and chewable tablets for adults. All household members, including adults and those without symptoms, should take a dose at the same time.

Mebendazole can be bought from pharmacies but is also available on prescription.

After taking the first dose of medication for threadworms, it is essential to follow the hygiene measures outlined above. Sometimes a second dose of medication is recommended two weeks after the first in case any eggs have been swallowed after the first dose.

What if I am pregnant or breastfeeding?


Pregnant women should not take medicines which kill worms during the first third of the pregnancy (first trimester). Hygiene measures alone may work and the worms die after about six weeks.

Provided that no new eggs are swallowed, no new worms will grow to replace them. Following the hygiene measures described above for six weeks should break the cycle of re-infection and clear the gut of threadworms.

If treatment with medication is considered necessary for threadworms when pregnant, a doctor may advise mebendazole in the second or third trimester but mebendazole is not licensed to be used during pregnancy.


If breastfeeding, six weeks of hygiene measures alone is the preferred treatment. If treatment with medication is considered necessary, a doctor may advise mebendazole.

but mebendazole is not licensed to be used in breastfeeding mothers.

Can a child with threadworms go to school?

Yes. There is no need to keep a child with threadworms off school, nursery, etc. The hygiene measures described above will mean that children will not have any eggs on their fingers when they go out from the home each day and so are unlikely to infect others.

Can you prevent threadworms?

General hygiene measures which reduce the risks of getting threadworms again are:

  • Washing hands and scrubbing under the nails first thing in the morning, after using the toilet or changing nappies, and before eating or preparing food.

  • Trying not to bite nails or suck fingers, and discouraging children from doing so.

  • If possible, avoiding sharing towels or flannels.

Further reading and references

  • Dunphy L, Clark Z, Raja MH; Enterobius vermicularis (pinworm) infestation in a child presenting with symptoms of acute appendicitis: a wriggly tale! BMJ Case Rep. 2017 Oct 6;2017. pii: bcr-2017-220473. doi: 10.1136/bcr-2017-220473.
  • Threadworm; NICE CKS, February 2023 (UK access only)
  • Pinworm Infection; Center for Disease Control and Prevention

Article history

The information on this page is written and peer reviewed by qualified clinicians.

  • Next review due: 25 Sept 2028
  • 27 Sept 2023 | Latest version

    Last updated by

    Dr Pippa Vincent, MRCGP

    Peer reviewed by

    Dr Doug McKechnie, MRCGP
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