Written for Stock My Medicine and clinically reviewed by Hajra Dhanchora, MPharm (GPhC 2216990).
Threadworms are the most common worm infection in the UK, and almost every family with a child at nursery or primary school meets them at some point. They're harmless, they're embarrassing for no good reason, and they're easy to kill. The part people get wrong is the second half of the treatment, the fortnight of hygiene that stops the eggs starting the cycle again. Here's how to spot them, treat the whole house in one go, and actually be rid of them.
Threadworm symptoms
The classic sign is intense itching around the bottom at night, when the female worms come out to lay their eggs, often waking a child or leaving them restless and irritable the next day. In girls the itching can extend to the vagina. You may see the worms themselves: tiny white threads, about a centimetre long, like bits of cotton, moving in poo, in the nappy or around the anus, most easily spotted with a torch an hour or two after the child falls asleep. Less common signs are poor sleep, bed-wetting in a child who'd stopped, skin irritation from scratching, loss of appetite and, rarely, tummy ache. Many people have no symptoms at all, which is why the whole household is treated.
How do you get threadworms?
By swallowing the eggs. The worm lays thousands of them on the skin around the bottom at night; they cause itching, the child scratches, the eggs lodge under the fingernails, and from there they reach the mouth, food, toys, towels, bedding, door handles and other children. Eggs survive for up to two weeks on surfaces and in dust, which is why a household keeps passing them round. Swallowed eggs hatch in the gut, the worms mature in a few weeks, and the cycle repeats. Pets don't carry threadworms; this is a human-only parasite, and it's not a sign of a dirty home.
Threadworm treatment: the tablet
A single dose of mebendazole kills the worms. It's sold from pharmacies as Ovex, as a chewable tablet or a banana-flavoured suspension for children who won't chew, and the family pack covers four people at once.
| Who | What to do |
|---|---|
| Everyone in the household aged 2 and over | One dose each, on the same day, whether they have symptoms or not |
| If symptoms return, or you know reinfection has happened | A second dose two weeks after the first; many pharmacists suggest this routinely |
| Children under 2 | Not over the counter; see a GP, who can prescribe mebendazole from 6 months or advise hygiene alone |
| Pregnant or breastfeeding | Hygiene measures alone in the first trimester; mebendazole can be used later or while breastfeeding on a GP's or pharmacist's advice |
Mebendazole works on the worms within a day or two, but it doesn't kill the eggs, which is why the next section matters more than the tablet. The itching may take a few days to settle as the last worms die; a dab of Sudocrem or a simple barrier cream soothes a scratched bottom in the meantime.
The hygiene that stops reinfection
Keep this up for two weeks after the tablet, or for six weeks if you're managing without medicine, because that's how long the eggs stay viable. It sounds like a lot; it's mostly things you half do anyway, done properly.
- Wash hands and scrub under nails after every toilet visit, before every meal and after changing nappies. Keep everyone's nails short.
- Shower or wash around the bottom first thing every morning to remove the eggs laid overnight. Morning, not evening.
- Close-fitting underwear at night, changed every morning, so the eggs can't scatter and scratching reaches fabric rather than skin. Pyjamas, not nightdresses, for girls.
- Change bedding, towels and nightwear daily for the first few days, then every few days, and wash at 60°C. Don't shake them out; it spreads eggs into the air.
- Damp-dust and hoover bedrooms, the bathroom and play areas, especially around the toilet, and wipe handles, taps, light switches and toys. Dettol-type disinfectants help on surfaces, but it's the wiping that removes eggs rather than the chemical.
- Stop nail-biting and thumb-sucking for the fortnight, as far as that's possible, and don't share towels or flannels.
- No food in bedrooms, and a separate towel per person.
Children don't need to miss nursery or school, and nurseries don't need to be told, though they often ask to be so they can remind other parents about handwashing.
Threadworms in adults
Adults catch them the same way, usually from a child in the house, and often have no symptoms beyond an occasional night-time itch they put down to something else. The treatment is the same single dose, and the hygiene applies to everyone, including the parent who does the laundry and the nappies. An adult with threadworms and no children at home has usually picked them up from a partner, a workplace with young children, or shared facilities, and should treat the whole household too. In women, the worms occasionally migrate to the vagina and cause irritation or discharge that gets mistaken for thrush; if a thrush treatment hasn't helped and the itch is worse at night, consider worms.
When to see a GP or pharmacist
A pharmacist can diagnose and treat threadworms without a GP. See a GP if the child is under two, you're pregnant, the infection keeps returning despite the full hygiene fortnight (occasionally a second or third household source needs finding), there's blood in the poo, weight loss, or symptoms that don't fit, since the itch can also be caused by thrush, eczema or piles. Worms that are larger, flat or segmented aren't threadworms and need a GP to identify. Our pharmacist can advise on dosing by age and weight and on what to do if someone in the house can't take mebendazole.
Frequently asked questions
Can threadworms go away on their own?
Each worm lives about six weeks, so a strict six weeks of hygiene with no re-swallowed eggs does clear them. In a household with children that almost never happens, which is why the tablet exists.
Can threadworms be dangerous?
No. They don't damage the gut and they can't kill you. The only real harm is lost sleep and, with prolonged scratching, a sore or infected skin patch.
How long does threadworm treatment take to work?
The worms die within a couple of days of the dose; itching usually settles within a week. If it's back after two to three weeks, that's reinfection from eggs, not failed treatment.
Can adults get threadworms?
Yes, usually from a child in the house, which is exactly why the whole family takes the dose together. Adults often have no symptoms and quietly keep the cycle going.
Can I catch threadworms from my dog or cat?
No. Threadworms only live in humans. Pets carry their own worms, which need their own treatment, but they're not the source of a child's threadworms.
Will Dettol kill threadworm eggs?
Disinfectants help on hard surfaces, but what removes the eggs is physically wiping and hoovering them away, washing at 60°C, and above all the handwashing that stops them reaching mouths. Don't rely on spraying alone.