Head lice: how to check and treat

Few things cause as much alarm at home as a note from school about head lice. The good news is that head lice are common, treatable and not a sign of poor hygiene. The NHS states plainly that head lice are not caused by dirty or short hair ¹, and MedlinePlus notes that hygiene has nothing to do with getting them ².

What are head lice?

Head lice are tiny insects that live in hair. Adult lice are about the size of a sesame seed ², up to 3mm long ¹. Their eggs, called nits, are brown or white and stuck firmly to the hair ¹. Nits are about the size of a dandruff flake and are often found near the neckline and behind the ears ².

They are most common in children aged about 3 to 11 ², but anyone can get them.

How they spread

Lice crawl. They cannot hop or fly ². They spread mainly by head-to-head contact ¹, such as when children play closely together. Spread through shared belongings like hats or hairbrushes is rare ², although DermNet still advises against sharing hats, combs and brushes ³.

Lice do not spread disease ².

Signs of head lice

• An itchy scalp, caused by an allergic reaction to the bites ²
• A tickling feeling of something moving in the hair ²
• Sores on the scalp from scratching, which can become infected ²
• Trouble sleeping, as lice are more active in the dark ²

Not everyone itches, so lice can be present for weeks before anyone notices.

How to check properly

The only way to be sure is to find a live louse ¹. Use a fine-toothed detection comb, available from pharmacies. Finding only nits is not enough: DermNet points out that white, empty nits do not contain live eggs and do not mean an active infestation ³.

Nits can be confused with dandruff, but nits stick to the hair shaft while dandruff flakes brush off easily. See dandruff treatment and dry scalp vs dandruff.

Treatment option 1: wet combing

Wet combing uses no chemicals and suits all ages. The NHS method is ¹:

• Wash the hair with ordinary shampoo.
• Apply lots of conditioner. Any conditioner will do.
• Comb the whole head with the detection comb, from roots to ends.
• Comb through everything a second time.

It takes about 10 minutes for short hair and 20 to 30 minutes for long, frizzy or curly hair ¹.

Repeat on days 1, 5, 9 and 13 to catch newly hatched lice, then check everyone again on day 17 ¹.

DermNet adds that combing in sections helps, and that combing should continue until no lice are found on three occasions in a row ³.

Treatment option 2: medicated lotions and sprays

If wet combing has not worked or is not suitable, medicated lotions and sprays from a pharmacy can be used. Lice should die within a day ¹. Some products need to be repeated after a week to kill lice that hatch later ¹. DermNet recommends at least two applications, 7 to 10 days apart, and prefers lotions to shampoos ³.

DermNet reports that 4% dimeticone, a silicone-based lotion that coats lice, cleared head lice in 69% to 92% of people after two applications a week apart, and that resistance is unlikely because it works physically ³.

Some older insecticides work less well because lice have become resistant. DermNet notes resistance to malathion, and that permethrin is no longer recommended in the UK for this reason ³.

MedlinePlus advises ²:

• Follow the product instructions exactly
• Use only one product at a time
• Ask a doctor first if you are pregnant or breastfeeding, or before treating a young child

Treatments that are not recommended

The NHS lists these as unlikely to work ¹:

• Products containing permethrin
• Head lice "repellents"
• Electric combs
• Plant oils, such as tea tree, eucalyptus and lavender oil
• Herbal remedies

The NHS also advises not using medicated lotions to prevent lice, as they can irritate the scalp ¹.

Treat the household, not just one child

Check everyone you live with or are in close contact with, and start treating anyone with lice on the same day ¹. DermNet also advises treating affected family members together ³.

There is no need to keep your child off school, and no need for a hot wash of all your laundry ¹.

Why treatment sometimes fails

DermNet lists the common reasons ³:

• Reinfestation from someone who was not treated
• Treatment not applied properly, or not repeated
• Resistance to the insecticide used
• Misdiagnosis, such as mistaking empty nits for active lice

Do lice cause hair loss?

Head lice do not usually cause hair loss. Heavy scratching can damage the scalp and cause sores ². If you notice patchy hair loss with scaling, especially in a child, it may be something else, such as scalp ringworm.

Can you prevent head lice?

The NHS says there is nothing you can do to fully prevent head lice. Regular wet combing with a detection comb helps catch them early and stop them spreading ¹.

When to get help

Speak to a pharmacist if lotions or sprays have not worked ¹. See a doctor if the scalp has infected sores, or before treating a baby or if you are pregnant ².

The bottom line

Head lice are common, harmless and not about hygiene. Confirm with a detection comb, treat everyone affected on the same day, and use either careful wet combing or a pharmacy lotion with a repeat application. For other causes of an itchy scalp, see itchy scalp.

Frequently asked questions

Do head lice mean my child's hair is dirty?

No. Head lice are not caused by dirty hair ^{1 2}.

Can head lice jump or fly?

No. They crawl and spread mainly by head-to-head contact ^{2 1}.

Do I need to keep my child off school?

No. There is no need to keep a child off school because of head lice ¹.

Does tea tree oil work for lice?

The NHS lists plant oils such as tea tree oil as unlikely to work ¹.

Educational content. Not medical advice.