What you are dealing with

Threadworms, also called pinworms, are tiny white worms that live in the bowel. The NHS describes them as looking like "pieces of white thread", and the HSE adds that they can be up to about a centimetre long. They are common in children and spread easily — the American Academy of Pediatrics calls the pinworm "essentially harmless", noting that it "causes more social concern than medical problems".

The itching has a mechanism. Female worms travel out of the bottom at night to lay eggs on the surrounding skin, and the eggs cause intense irritation. That is why the itch is worse in bed, and why a child who was fine all day is suddenly inconsolable at 9pm.

How to know

The NHS says you can spot threadworms in poo, and may also see them around a child's bottom, since "the worms usually come out at night while your child is sleeping." The HSE adds that you may find them on bedclothes or sheets. RCH Melbourne suggests shining a torch on the area at night, and makes the practical point that "if your child has an itchy bottom, there is a good chance they have threadworms."

Other signs the NHS lists are extreme itching around the anus or vagina, particularly at night, and irritability and waking during the night. Less common signs include weight loss, bedwetting and irritated skin around the anus. RCH notes that threadworms can also cause or worsen soreness and itching of the vulval area in girls.

Treatment: what the guidance actually says

The NHS route is the pharmacy, not the GP: "a pharmacist can help with threadworms", and treatment can be bought without a prescription. The instruction that surprises people is that treatment is not just for the child with symptoms. The NHS says to treat everyone over 2 years old in the household, "even if they do not have symptoms". The HSE says to treat everyone in the household. RCH explains why: adults often catch threadworms from children, and eggs survive up to two weeks outside the body.

This page does not give amounts. Follow the instructions on the pack or the advice of your pharmacist, and tell them your child's age. The NHS reminder about medicines for children applies here as much as anywhere: always read the label, stick to the recommended dose, and check with a pharmacist, health visitor or GP if you are unsure.

When to see a GP instead of a pharmacist

There are three published exceptions.

Children under 2. The NHS says to tell the pharmacist if you need to treat a child under 2, because "treatment might not be suitable and you may need to speak to a GP". The AAP says the same from the other side, noting that the usual medication "is not recommended for use in children under two years of age". The HSE lists a child under 2 as a reason to see a GP.
Pregnancy and breastfeeding. Both the NHS and the HSE say to speak to a GP or tell the pharmacist if you are pregnant or breastfeeding.
Treatment that has not worked. The HSE says to see a GP if you still have signs of infection a month after treatment. RCH advises seeing a doctor if several weeks of over-the-counter treatment have not resolved it.

The NHS also notes that if you cannot take the medicine, threadworms can be cleared by hygiene measures alone — but that takes 6 weeks rather than 2.

The hygiene fortnight

Medicine kills the worms but not the eggs, and eggs can live up to two weeks outside the body. The NHS says to follow these measures for 2 weeks if you are taking medicine, or 6 weeks if you are not.

Wash hands and scrub under fingernails, particularly before eating and after using the toilet or changing nappies.
Shower or bathe every morning, which removes eggs laid overnight.
Rinse toothbrushes before using them.
Keep fingernails short.
Wash sleepwear, sheets, towels and soft toys at a hot temperature every day for several days after treatment. The HSE notes that 60 degrees Celsius kills threadworm eggs, but says to check the care label for each item.
Disinfect kitchen and bathroom surfaces using hot water.
Vacuum, and dust with a damp cloth.
Make sure everyone wears underwear at night and changes it in the morning.
Do not shake clothing or bedding, which scatters eggs onto other surfaces.
Do not share towels or flannels.
Discourage nail biting and thumb or finger sucking.

Pyjama bottoms and close-fitting underwear at night are worth adding, because they physically reduce night scratching and the eggs that end up under fingernails.

Nursery, school and blame

The NHS is unambiguous: "if you or your child has threadworms there's no need to stay off nursery, school or work." Guidance differs between countries — RCH advises keeping a child home until they have been treated — so follow your local service.

Reinfection is normal, not a sign of failure. The NHS explains that children can get threadworms again after treatment if they swallow eggs, which is why hand washing matters more than any deep clean. And you cannot catch them from the dog: RCH states plainly that "you cannot catch threadworms from animals", though the AAP suggests hand washing after playing with pets since eggs can be carried in fur.

Nurseries are the usual route of transmission and no amount of cleaning at home prevents that. The AAP is candid that "it is very difficult to prevent pinworms", and suggests encouraging hand washing after using the toilet and asking a childminder or nursery to wash toys frequently if worms have been found in one or more children. Threadworms are not a verdict on how clean a house is; they are a consequence of small children sharing space, floors and toys.

The cycle, and why timing matters

Understanding the life cycle explains why one dose and one wash are not enough. The NHS describes it: eggs are swallowed, the larvae hatch in the gut, and they take 1 to 2 months to mature into threadworms. Eggs survive up to 2 weeks outside the body. That gap between swallowing an egg and having an itchy child is why symptoms often reappear a few weeks after what looked like a successful treatment.

RCH notes that most treatments recommend repeating the dose for all family members one or two weeks later, and that a third round can be considered if infections keep recurring in a family. Ask your pharmacist about repeat timing when you buy the treatment, rather than working it out afterwards.

Finally, if the itching does not settle after treatment and hygiene measures, it is worth having the skin looked at rather than assuming worms again. Threadworms are the most common cause of an itchy bottom at this age but they are not the only one, and a GP can tell the difference between eggs, a skin condition and simple soreness from scratching.

Toddler Itchy Bottom at Night: Threadworms Explained