Head lice and nits: how to spot them and get rid of them

NICE Clinical Knowledge Summaries describe head lice as wingless parasitic insects that live in the hair of the human head and feed on blood from the scalp. The NHS says they are up to 3mm long and can be difficult to spot in the hair. Eggs, called nits, are brown or white and stuck to the hair shaft. An infestation usually involves fewer than 10 live lice, according to NICE CKS, and left untreated it may last a long time.

Head lice do not jump or fly; they crawl from one head to another during close contact, which is why they are especially common in young children and their families.

Itching is a common sign but not proof. NICE CKS says detection combing, which is systematic combing of wet or dry hair with a fine-toothed comb with teeth 0.2 to 0.3 mm apart, is the best way to confirm lice, and that active infestation should only be diagnosed if a live louse is found. The presence of eggs alone, hatched or not, does not prove an active infestation, and a person should only be treated if a live louse is found.

Detection combs are sold online and in pharmacies. NICE CKS also recommends that primary-school-age children are examined regularly at home with a detection comb so that infestations are found early.

The NHS says to treat head lice as soon as you spot them, to check everyone you live with or have close contact with, and to start treating anyone with lice on the same day. Treatment can be done without seeing a GP. The usual wet combing method is:

• Wash the hair with ordinary shampoo.

• Apply lots of conditioner (any kind).

• Comb the whole head from the roots to the ends with the detection comb.

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

• Comb through all the hair a second time when finished.

• Repeat on days 1, 5, 9 and 13 to catch newly hatched lice, and check that everyone is lice-free on day 17.

If wet combing has not worked or is not suitable, the NHS says you could try a medicated lotion or spray from a pharmacy, supermarket or online. They kill head lice in all types of hair, and lice should die within a day. Some products need repeating after a week to kill newly hatched lice. Check the pack to see whether the product is suitable for you or your child, and how to use it. If a lotion or spray does not work, speak to a pharmacist about other treatments.

NICE CKS names the types in use: a physical insecticide such as dimeticone 4% lotion, a traditional insecticide such as malathion 0.5% aqueous liquid, or wet combing. It advises that no treatment can guarantee success, but each has the best chance when used correctly and when all affected household members are treated on the same day. Detection combing after treatment confirms success.

If a live louse is still found after treatment, NICE CKS suggests checking the treatment was used correctly, looking for sources of reinfestation among household members, close family and friends, and then either repeating the same treatment or trying a different one, bearing in mind possible resistance to malathion.

The NHS lists treatments that are not recommended because they are unlikely to work: products containing permethrin, head lice repellents, electric combs, plant oil treatments such as tea tree, eucalyptus and lavender oil, and herbal remedies. NICE CKS says essential-oil and herbal treatments are not recommended because of the lack of good-quality evidence on safety and efficacy.

Medicated lotions and sprays should not be used to try to prevent lice, since the NHS warns they can irritate the scalp.

The NHS says there is no need to keep a child off school with head lice and no need for a hot wash of laundry. NICE CKS gives the reason for the laundry advice: once detached from the head, a louse lives only 1 to 2 days, so clothing and bedding do not need washing at high temperature or fumigating.

Both sources stress that you cannot prevent head lice. The practical approach is regular detection combing, particularly for primary school children, telling close contacts so they can check too, and treating all affected household members on the same day.

Speak to a pharmacist if lotions and sprays have not worked, or if you are unsure whether a product suits a baby, pregnant woman or someone with a scalp condition. A GP is worth seeing if the scalp is sore, weeping or crusted, which may mean the skin has become infected from scratching.