Head Lice

What head lice are

The head louse (Pediculus humanus capitis) is a grayish-white to tan insect about 2 to 3 mm long when adult, roughly the size of a sesame seed. It cannot jump or fly. It crawls quickly and holds tight to hair with claw-like legs. Its life cycle:

Empty nit shells stay attached to the hair and move away from the scalp as hair grows. Nits found more than about 1 cm (half an inch) from the scalp are usually already hatched or dead.

How head lice spread

• direct head-to-head contact, by far the most common route: playing, hugging, sleepovers, sports
• less often, sharing hats, scarves, hairbrushes, helmets, pillows or headphones

Head lice do not live on pets. They are common in all social groups and are not a sign of poor hygiene. Clean hair does not protect against them.

Symptoms

• itching of the scalp, caused by an allergic reaction to louse saliva. It may not start for 4 to 6 weeks after a first infestation, and some people never itch
• a tickling feeling of something moving in the hair
• small red bumps or scratch marks on the scalp, neck and shoulders, which can become infected (impetigo)
• trouble sleeping, as lice are more active in the dark
• sometimes, swollen glands at the back of the neck

Nits vs dandruff and other lookalikes

Scalp itching without lice is often caused by seborrheic dermatitis (dandruff) or a fungal infection such as tinea capitis. Intense itching elsewhere on the body, worse at night, suggests scabies instead.

Diagnosis

The most reliable way to confirm head lice is to find a live louse. Wet combing works best:

1. wash and condition the hair, leaving the conditioner in
2. detangle with a regular comb
3. comb section by section from the scalp to the tips with a fine-toothed lice comb
4. wipe the comb on a white tissue after each stroke and look for lice

Nits alone, especially those far from the scalp, do not prove an active infestation.

How to get rid of head lice

Over-the-counter treatments

• permethrin 1% lotion
• pyrethrins with piperonyl butoxide
• ivermectin 0.5% lotion (available over the counter in the US), applied once to dry hair
• dimeticone-based products, which work by coating and suffocating lice (common outside the US)

Follow the label exactly. Many products need a second application 7 to 10 days later to kill newly hatched lice. Lice resistance to permethrin and pyrethrins is common in many areas.

Prescription treatments

• spinosad 0.9% suspension
• malathion 0.5% lotion (flammable; keep away from heat and flames)
• oral ivermectin in selected cases

Lindane is no longer recommended because of toxicity.

Combing

Wet combing every 3 to 4 days for 2 weeks helps remove lice and nits and checks whether treatment worked. It can also be used alone, but needs persistence.

What does not work

There is no good evidence for mayonnaise, olive oil, essential oils or "smothering" home remedies. Never use kerosene, gasoline or pet lice products, which are dangerous. Shaving the head is unnecessary.

Cleaning the home

Lice die quickly off the head, so extensive cleaning is not needed. The CDC suggests:

• washing bedding, hats and clothing used in the 2 days before treatment in hot water (at least 130 °F, 54 °C) and drying on high heat
• sealing items that cannot be washed in a plastic bag for 2 weeks
• soaking combs and brushes in hot water for 5 to 10 minutes
• vacuuming furniture and floors

Insecticide sprays for the home are not recommended.

School and household

• check all household members and treat only those with live lice
• the American Academy of Pediatrics advises that children should not be sent home early or kept out of school because of head lice; treatment can start after school
• "no-nit" school policies are not recommended

Prevention

• avoid head-to-head contact during play and sports
• do not share hats, scarves, brushes, combs, hair ties or helmets
• check children's hair regularly, especially after sleepovers or when lice are reported in school

Frequently asked questions

What are the signs of head lice?

The main sign is an itchy scalp, especially behind the ears and at the back of the neck. You may see live lice moving in the hair or nits glued to hair shafts close to the scalp. Small red bumps from scratching are common.

How do you get rid of head lice fast?

Use a lice treatment such as permethrin, ivermectin lotion or spinosad, following the label, and comb the wet hair thoroughly with a fine-toothed nit comb. Repeat treatment or combing as directed to catch newly hatched lice.

How do you tell nits from dandruff?

Nits are glued firmly to one side of the hair shaft and do not move when you blow on them or brush them. Dandruff flakes are irregular and come off easily. Nits are usually found close to the scalp.

Can adults get head lice?

Yes. Adults, especially parents and caregivers of young children, can get head lice through head-to-head contact. Treatment is the same as for children.

Do I need to clean my whole house for head lice?

No. Lice cannot survive long off the scalp. Wash recently used bedding, hats and brushes, bag items that cannot be washed for 2 weeks, and vacuum. Fumigation and household sprays are unnecessary.