Head lice are tiny parasites that live on the human head and feed on blood from the scalp. They are common in children and spread as a result of head-to-head human contact, not through pets.
Head lice are neither dangerous nor a sign of poor hygiene, and they do not spread any diseases. The main symptom of lice is itching.
People can treat a head lice infestation with over-the-counter (OTC) or prescription medication, which will kill the head lice.
Head lice have six legs and are usually grayish-white or tan. However, they can camouflage, so they may appear darker or lighter to match different hair colors.
Head lice have three stages in their lifecycle:
- eggs, which people often refer to as nits
- adult head lice
A nymph hatches from the egg and goes through several stages of growth before turning into an adult head louse. Nymphs look similar to adult head lice but are smaller, roughly the same size as a pinhead.
Adult head lice are about 2–3 millimeters (mm) in length, which is roughly the size of a sesame seed. Head lice crawl and cannot fly or jump.
People may need a magnifying glass to see head lice in detail.
The eggs, or nits, are tiny ovals that stick to the hair shaft, measuring 0.8 mm by 0.3 mm.
Female head lice lay the eggs within 6 mm of the scalp. People will often find them behind the ears and on the back of the neck.
The term nits can also refer to the empty egg casings that remain in the hair once the nymph has hatched. These are easier to see, especially on darker hair, as they are lighter, usually white or yellow.
The most common symptom of head lice is an itchy head. The itchiness is the result of a local allergic reaction to the lice bites.
People with head lice may also notice the following symptoms:
- a tickling sensation on the head
- the feeling of something moving on the head or through the hair
- difficulty sleeping as head lice become more active in darkness
- sores on the head from scratching
It is possible to develop an infection in the sores from scratching the head. People will need to see their doctor if they get a scalp infection.
Other conditions or items in the hair may look similar to head lice. People can sometimes mistake hairspray droplets, scabs, or dirt for nits.
Some other issues that can resemble head lice include:
Hair casts are white, tube-like debris, and they surround the hair shaft. They are usually 2 to 8 mm in length. They are uncommon and often have an association with other skin conditions.
Hair casts slide easily along the hair, whereas nits stick to it and are harder to remove. People may be able to remove hair casts with coal tar shampoo or a fine-toothed comb.
People with light-colored hair should be careful about using coal tar shampoo as it can discolor the hair.
Dandruff can look similar to head lice eggs and also causes the scalp to itch. Dandruff is a scalp condition in which dry skin comes away from the scalp in white flakes.
Dandruff lies on the scalp and comes away easily, whereas nits stick to the hair.
People can treat dandruff effectively using a dandruff shampoo. Dandruff shampoos are available in drug stores and online.
Mites are small insects that cause scabies by digging into the skin and irritating it, which makes the skin itchy. Scabies usually affects the fingers, ankles, or wrists rather than the head.
People who notice a rash and uneven red lines on the skin or scalp might have scabies and should see their doctor, who may prescribe a topical cream as treatment.
To treat a head lice infestation, people can use medicines called pediculicides, which kill head lice. Some treatments are not suitable for young children, so it is best to check with a doctor or pharmacist before using them.
People can apply OTC head lice treatment topically to the head. It is important to follow the instructions on the medicine, which may advise a person to:
- wash the hair and dry it with a towel to remove excess water
- use a nonconditioning shampoo, as conditioner can create a barrier between the hair and the treatment
- follow the instructions on how long to leave the treatment on the hair
- rinse the hair over a sink instead of in the bath or shower to stop the treatment causing any irritation to the rest of the skin
- use warm rather than hot water
The treatment may cause a mild burning or irritating feeling. Afterward, people should use a nit comb to remove any dead or live lice that remain as well as the eggs.
Both of these treatments only kill live head lice, not the unhatched eggs, so people may need to apply a second dose of treatment 9 to 10 days after the initial one.
If OTC solutions are not effective, people can see their doctor. They may need to use prescription medicine that contains:
- benzyl alcohol
People should follow their doctor's instructions when applying prescription head lice treatment, as misusing or overusing it may cause side effects.
Alongside treatments, people can take action to help limit lice and prevent a reinfestation, though treating all household members with active lice at the same time is usually sufficient. Some tips for prevention include:
- washing any items of clothing or bedding that people have used in the last couple of days in a hot wash above 128.3°F (53.5°C) to kill the lice
- vacuuming floors and furniture onto which people with head lice may shed hair
- avoiding sharing any hair accessories, clothing, or items that come in contact with the head of a person with lice
Head lice can only survive for up to 2 days away from the human head, so they will not last long in any surrounding areas.
Shampoos for head lice are available for purchase in drug stores, pharmacies, and online.