When it happens · 4 min read
Bottom itching that's worse at night
Your child cannot stop scratching, and it is far worse at night than during the day. They are waking up, they are irritable, and nobody warned you about this one because it is the childhood infection people are quietly embarrassed by.
Pinworms — threadworms, if you grew up outside the US — are extremely common in preschoolers and spread easily between children who are playing normally. The treatment is straightforward. The reason it comes back is almost always that a specific step got skipped.
Last updated August 17, 2026
Why it's worse at night
The female worms travel out to lay their eggs around the anus at night. That is the entire explanation for the symptom pattern, and it is what makes night-time itching so much more suggestive than daytime itching.
You can often see them. Fine white threads, a few millimetres long, around the bottom or in the stool. The classic method is looking with a torch an hour or two after they have fallen asleep. Your pediatrician may also confirm it with a tape test, done first thing in the morning before any washing.
In girls, the irritation can extend to the vulva, and that gets mistaken for a urine infection more often than you would expect. Plenty of children have no symptoms at all, which is exactly why it moves through a whole class.
The two steps people skip
Treatment is usually a single dose of medication, repeated two weeks later. That second dose is not optional and it is the one people forget. The medication kills the worms but not the eggs, so the repeat dose is what catches the ones that have hatched since — skipping it is the single most common reason it comes straight back.
The other step is treating the whole household at the same time, symptoms or not. Treating one child alone rarely works, because the people around them are very likely carrying it without knowing.
What to do on treatment day
Wash all bedding, nightwear and towels on a hot wash, and vacuum thoroughly. Collect the linen carefully rather than shaking it out, which just puts eggs into the air.
Then keep it up for two weeks after the last dose: handwashing after the toilet and before food, attention to under the fingernails, and nails kept short — that is where the eggs travel. Pajamas and underwear at night so scratching does not deliver eggs straight onto hands, and a shower or bath in the morning to rinse off overnight eggs.
What this is not
It is not a sign of a dirty home, poor hygiene, or anything you did wrong. It is a sign of a child who plays with other children and puts their hands near their face, which is every child.
It is also worth telling nursery or preschool, not because your child needs to stay home — they do not — but because it is almost never a single case.
Common questions
- Do I really have to treat everyone, even the adults?
- Yes. The CDC's guidance is to treat the infected person, their caregivers and household members at the same time. Adults carry it without symptoms, and treating the child alone is the usual reason it returns a month later.
- Can they go to preschool?
- Yes. Pinworms do not require exclusion. Tell the setting so they can let other families know, and keep up the handwashing.
- It came back anyway. What went wrong?
- Almost always one of three things: the second dose was missed, someone in the house was not treated, or the two-week hygiene routine stopped after a couple of days. Reinfection is far more common than treatment failure.
If it's this, not that
Still not sure
This page is the general answer. Yours is a specific child.
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Where this comes from
- Pinworms - how to spot them and how they're treatedAAP
- Preventing pinworm - the second dose, the whole household, and the two weeks afterCDC
Every claim on this page traces to one of these. See every source we use →
Written from the sources named above, and it is not a substitute for your own doctor. If something feels wrong to you, that instinct is a good enough reason to call — you know yourself and this family better than any page does.