Head Lice
2-minute consultation reviewed by a UK clinician
We check your answers and recommend a suitable option
Plain packaging to your door, fast and confidential
Head Lice: Checking, Treating and What Actually Works
Why only a live louse justifies treatment, why the second application matters more than the first, and the household effort that is entirely wasted.
Key fact: Only treat if you find a live louse. Nits — the empty egg cases glued to the hair — can stay stuck there for months after an infestation has gone, and treating on the strength of nits alone is the commonest reason households treat repeatedly for something that is no longer there.
What head lice are
Head lice are small wingless insects that live on the scalp and feed on blood. An adult louse is about the size of a sesame seed, black, brown or grey-white, and it crawls — it cannot jump or fly. They live only on human heads and die within a day or so away from one.
They have nothing to do with hygiene, hair length, or how often hair is washed. Clean hair is no barrier at all.
| Term | What it means |
|---|---|
| Louse | The live insect. Finding one is what justifies treatment |
| Eggs | Laid close to the scalp, brown, and viable. They hatch in about 7 to 10 days |
| Nits | The empty white egg cases left behind after hatching. They stay glued to the hair as it grows out and can persist for months. They are evidence of a past infestation, not a current one |
Only a live louse counts
No treatment should be carried out unless a live louse is found. This is the single most important rule in the topic. Itching alone is not enough, nits are not enough, and a letter home from school is not enough. Treating without confirming means using an insecticide on a child who does not need it, repeatedly, which is how resistance builds and how families end up treating every few weeks all term.
Detection combing is how you find out. How to check for head lice sets out the method properly — it is more than twice as fast and over three times more effective than looking through the hair by eye.
How they spread
- Head-to-head contact, and essentially only that. Lice crawl from one head to another where hair touches hair for long enough
- Within families as much as at school — sofas, bedtime stories and selfies all involve heads touching
- Not from bedding, clothing, hats or furniture in any meaningful way. There is no evidence that lice are transmitted any way other than head to head
- Not from pets, which cannot carry human head lice
- Commonest in children aged 4 to 11, and in the adults who live with them
The practical consequence: boil-washing the bedding, bagging the soft toys and hoovering the sofa achieve nothing. That effort is better spent on combing everyone's hair properly.
Symptoms
- Itching — an allergic reaction to louse saliva, which can take weeks to develop after lice first arrive, and can persist for weeks after they have gone
- A feeling of something moving in the hair
- Irritability or poor sleep in a young child
- Small red bumps on the scalp, neck or behind the ears from scratching
- Frequently nothing at all — many children have no symptoms, which is why detection combing matters more than waiting for itching
Because the itch lags so far behind, itching is unreliable in both directions: a child can have lice for weeks without itching, and can itch for weeks after successful treatment.
How to check
Detection combing with a fine-toothed comb — teeth spaced 0.2 to 0.3mm apart, which is much finer than an ordinary nit comb sold alongside some products.
- Wet hair with conditioner makes it easier, because conditioner stops lice moving and lets the comb through
- Comb the whole head at least twice, from the scalp outwards, checking the comb after every stroke
- Wipe the comb on white kitchen roll to see what comes out
- About 10 minutes for short hair, 20 to 30 minutes for long, frizzy or curly hair
- Do it in good light, ideally daylight
Treatment
| Approach | How it works | Typical use |
|---|---|---|
| Physical insecticides — dimeticone 4%, isopropyl myristate | Coat and suffocate or dehydrate the louse, physically rather than chemically, so resistance is not expected | Applied to dry hair; contact times vary from 10 minutes to overnight depending on the product. Repeat after 7 days |
| Traditional insecticide — malathion 0.5% aqueous, as Derbac-M | A chemical insecticide that kills lice | Applied for 12 hours or overnight. Repeat after 7 days. Resistance has been reported |
| Wet combing | Physically removes lice with conditioner and a detection comb — no chemicals at all | Sessions on days 1, 5, 9 and 13, with a check on day 17 |
All three are reasonable. Wet combing is free, has no side effects and suits pregnancy and very young children, but it demands real persistence. Treatments compared covers how to choose, and what to do when one has not worked.
Why a second application matters
Most treatments kill lice well but kill eggs less reliably. Eggs already laid hatch over the following week — so a single application leaves a new generation to emerge a few days later, and the infestation looks as though it never cleared.
Repeat the treatment after 7 days unless the product specifically says otherwise. Skipping the second application is the commonest reason head lice appear to come straight back, and it gets blamed on reinfection from school.
School
There is no need to keep a child off school for head lice. They are not a reason for exclusion, and by the time they are found they have usually been there for weeks.
What does help is treating promptly once live lice are confirmed, and telling close contacts so they can check. School, spread and what does not work covers this, including what to do about the class letter.
What does not work
- Repellent sprays and "preventive" products — there is nothing you can do to prevent head lice
- Permethrin-containing products — resistance is widespread and they are not recommended
- Electric combs and vacuum devices
- Tea tree, eucalyptus, lavender and other plant oils — unlikely to work, and some irritate the scalp
- Shampoo formulations — too dilute and in contact for too short a time
- Washing bedding, bagging toys, hoovering — lice do not spread that way
- Treating the whole family "just in case" — treat only those with live lice
Who else needs checking
- Everyone in the household, and anyone in close head-to-head contact in the past month
- Check on the same evening, so an infested head is not left untreated to reinfect the others
- Treat only those with live lice found
- Tell close contacts outside the house — sleepovers, grandparents, close friends — so they can check too
- Recheck everyone after treatment, 2 to 3 days after the final application and again about a week later
Speak to a pharmacist or GP before treating if: the child is under 6 months; you are pregnant or breastfeeding; there is asthma or eczema, since some preparations can irritate or contain alcohol; the scalp is broken, weeping or crusted, which may indicate a secondary skin infection; or treatment has failed twice despite being used correctly.
Frequently Asked Questions
How do I know if my child has head lice?
Only by finding a live louse. Detection combing with a fine-toothed comb through conditioned wet hair is the reliable method, and it is over three times more effective than looking by eye. Itching is unreliable, because it can take weeks to develop and can persist for weeks after lice have gone.
Are nits the same as head lice?
No. Nits are the empty egg cases left after eggs have hatched, and they stay glued to the hair for months as it grows out. They show a past infestation, not a current one. Treatment should only be used when a live louse has been found.
Do head lice spread from bedding or hats?
Not meaningfully. There is no evidence that lice are transmitted any way other than head-to-head contact, and they die within about a day away from a scalp. Washing bedding, bagging toys and hoovering achieve nothing, and the effort is better spent combing everyone's hair.
Do I need to keep my child off school?
No. Head lice are not a reason to keep a child off school. Treat promptly once live lice are confirmed, and tell close contacts so they can check their own children.
Why do head lice keep coming back?
Most often because the second application was skipped. Treatments kill lice more reliably than eggs, and eggs already laid hatch over the following week, so treatment is repeated after 7 days. Other reasons are an untreated household member and treating without ever confirming live lice.
Can you prevent head lice?
No. There is nothing that reliably prevents them, and repellent sprays and preventive products are not recommended. Regular detection combing does not stop lice arriving but catches them early, when there are fewer of them and less has been passed on.
References
- NHS. Head lice and nits. nhs.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Head lice. cks.nice.org.uk
- Welsh Medicines Information Centre. Head Lice: Questions and Answers for Healthcare Professionals. wmic.wales.nhs.uk
- UK Health Security Agency. Health protection in children and young people settings, including education. gov.uk
- Burgess IF et al. Randomised, controlled, assessor blind trial comparing 4% dimeticone lotion with 0.5% malathion liquid for head louse infestation. PLoS ONE 2007. journals.plos.org
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Head lice treatment should only be used when a live louse has actually been found, and product instructions vary, so always read the leaflet supplied. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
