Threadworm: Why You Treat the Whole House, Not Just the Child

Threadworm is extremely common in children, completely harmless, and nothing to do with cleanliness. The reason it keeps coming back in some households is almost always the same: one person was treated instead of everybody, or the two weeks of hygiene measures that go alongside the tablet were skipped.

How it spreads

Threadworms live in the bowel. At night the female comes out to lay eggs around the anus, which causes the intense itching that is the classic symptom. Scratching transfers eggs onto fingers and under nails, and from there onto anything touched — door handles, toys, bedding, food.

Eggs survive up to two weeks outside the body, and are easily swallowed by the next person. That is the whole cycle, and it is why one treated child in an untreated household simply gets it again.

Signs to look for: itching around the bottom, worse at night, disturbed sleep, and sometimes irritability. In girls, itching around the vagina can occur. You may see the worms themselves — white, thread-like, roughly a centimetre long — in the stool or around the anus, best checked with a torch a couple of hours after the child goes to sleep.

Treating it properly

Mebendazole is the usual treatment and is available from the pharmacy for anyone aged two and over. A single dose is normally enough, with a second dose two weeks later if symptoms return.

Treat everyone in the household at the same time, including adults and anyone without symptoms. Many people carry threadworm without noticing, and leaving them untreated keeps the cycle going.

Mebendazole is not suitable in pregnancy, while breastfeeding, or for children under two — in those cases hygiene measures alone are used for six weeks, and you should speak to us or your GP first.

The hygiene fortnight

The tablet kills the worms. It does not touch the eggs already scattered around the house, so the following matters for two full weeks:

• Wash all bedding, nightwear and towels on a hot wash on day one — do not shake them, which spreads eggs into the air.
• Vacuum and damp-dust thoroughly, especially bedrooms.
• Bath or shower every morning, washing around the bottom first thing to remove eggs laid overnight.
• Wash hands and scrub under nails before every meal, after using the toilet, and first thing in the morning.
• Keep nails short; discourage nail biting and thumb sucking.
• Wear close-fitting underwear at night, changed every morning.
• Do not share towels or flannels.
• Keep toothbrushes in a covered cabinet and rinse before use.

When to get advice

Come and see us if symptoms persist after a second dose, if the person needing treatment is under two, pregnant or breastfeeding, or if there is bleeding, significant abdominal pain, weight loss or a rash. Threadworm does not cause those, so they need a different explanation.

Children do not need to stay off school, and there is no need to tell anyone beyond the household unless you want to.

Frequently asked questions