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Head lice: how to spot them, how to treat them

Carol Coley
RN BSc(Hons)
Skin Cancer Nurse Specialist
Hospital NHS Trust

Head lice (pediculosis capitis) are small greyish parasitic animals that live only on human scalps and die in a day or two if away from the human scalp. They cannot fly, jump or burrow into the scalp, but their six legs are perfectly adapted for clinging firmly onto scalp hairs. Their presence does not imply a lack of cleanliness. Head lice can affect anyone - rich or poor, well washed or not.(1) It is a common mistake to associate head lice with dirty hair as they are equally happy living in clean hair.(2) Head lice are most common in children between the ages of four and eleven. They are more common in girls than boys, but can affect anyone.

How is it spread?
Head lice are usually picked up by head-to-head contact with an infected person. It takes about 30 seconds for a louse to transfer from one scalp to another. Shared hats, combs or pillows can also aid their spread. Head lice can be found in all types and lengths of hair. Head lice infestation is not hereditary, but several members of a family may have them at the same time. Most people with head lice do not have any symptoms. An itchy scalp occurs in about one in three cases. It often takes about three months for itch to develop after being infected. That is why many people do not notice that they have head lice for a while, and may have been passing them on to others for some time. Head lice and nits do not wash off with normal shampoo.(3)
Female head lice live for up to 40 days, during which time they can lay more than 100 eggs. They cement their eggs to hairs at the point where they grow out of the scalp surface. The eggs are oval, yellow or white, and take seven to 10 days to hatch out. The empty egg cases (nits) remain stuck onto the hairs, and it is possible to work out roughly how long the lice has been present by the distance the nits have grown out from the scalp surface. The eggs that still contain unborn lice usually lie within half a centimetre of the scalp surface. The newly hatched young lice (nymphs) pass through several stages of development over the next week or two before they become adults.(1) A fully grown head louse is about 2mm long (about the size of a sesame seed).(2)
Head lice have to feed on human blood several times a day to survive, and the bites, saliva and faeces often make the scalp itchy. Some people feel that there is something moving on their scalp. If there is a large number of lice, itching may be intolerable and can cause secondary infection (impetigo and pustules).(4) However, many of those who have head lice are not itchy and have no symptoms. The lack of itching does not mean that head lice are not present; the only way to be sure is by taking a careful look at the scalp.

How to detect head lice
It i bests difficult to find head lice just by looking. Detection combing or bug busting is the way of confirming their presence. The procedure for this is as follows:(3)

  • Wash the hair in the usual way with ordinary shampoo.
  • Rinse out the shampoo and put on lots of ordinary conditioner.
  • Comb the hair with a normal comb to get rid of tangles.
  • Once hair is tangle-free, switch to a detection comb. This is a special fine-toothed comb that you can buy in pharmacies. (The teeth of normal combs are too far apart.)
  • Slot the teeth of the detection comb into the hair at the roots so that it is touching the scalp gently.
  • Draw the comb through to the tips of the hair. The detector comb removes the lice, which cannot grip hair that is slippery with the conditioner.
  • Repeat this in all directions until all the hair has been combed.
  • Check the comb for lice after each stroke. A magnifying glass may help.
  • If any lice are seen, clean the comb by wiping it on a tissue or rinse it before the next stroke.
  • Comb the hair over a white surface such as white paper, so that any head lice that are flicked out by the comb are easy to see.
  • After the whole head has been combed thoroughly, rinse out the conditioner.
  • Comb the wet hair with the normal comb to get rid of tangles and repeat the detection combing again to check for any lice that might have been missed the first time.

It normally takes 10-15 minutes to do detection combing properly, depending on how thick the hair is.
Bug busting is a way of removing head lice without using any lotion or cream rinse to kill them.(3) It can be very effective, but is not yet supported by published scientific evidence.(5) It needs to be done on every member of the household who has head lice and should be repeated every four days for at least two weeks.
The first combing should remove all hatched head lice, but it does not remove eggs. Any young lice that hatch from eggs after the first session are removed during the second, third and fourth bug-busting sessions.
If there are any full-grown lice at the second, third or fourth session, it means that either some head lice were missed on the first session or there has been reinfection from someone else. If this happens, the number of bug-busting sessions needs to be increased, and where adult lice are seen a further three sessions need to be done at four-day intervals until no adult lice are seen.(3) The nits may remain after the lice have gone, but they will eventually fall out, or a fine-tooth nit comb can be used to remove them.
A common reason for head lice to recur in one person is because close contacts (family and close friends) are not checked for head lice, and not treated if they are infected. The treated person is then likely to get head lice back again from untreated family or friends.

There are a number of proprietary, active products available to treat head lice.(5) The chemical insecticides include:

  • Malathion (eg, Quellada M; GlaxoSmithKline).
  • Phenothrin (eg, Full Marks; SSL).
  • Permethrin (eg, Lyclear; Pfizer).

These are available over the counter and should only be used for confirmed cases of head lice due to the potential side-effects caused by strong chemicals, such as scalp irritation. These insecticides are generally lotions, liquids or cream rinses. The most effective insecticides are alcohol-based lotions, but these are not suitable for everyone, particularly those with eczema or asthma.(2) The instructions on how to apply these insecticides need to be followed carefully. They are usually rubbed onto the scalp and hair and left for a minimum of 12 hours before being washed out. This will kill living lice, but the treatment needs to be repeated a week later to destroy any lice that have hatched since the first treatment.(5) Of all the chemical insecticides, the one that best stands up to scientific scrutiny is permethrin 1%,(6) but it is possible for head lice to develop resistance to one or more insecticides. There is a stronger type of insecticide, carbaryl (eg, Carylderm; SSL), which is only available on prescription in cases where infections are not cleared by other insecticides.(2)
It is advisable not to use antilice lotions to prevent head lice, or just in case there are any. Keep children away from fires, lighted cigarettes and other flames while being treated with the alcohol-based lotions as they are flammable and some children have been badly burnt as their hair has caught fire while being treated.(3)
There are alternative treatments to treat head lice. These include essential oils (including tea tree), herbal extracts and homeopathic tinctures. There is no scientific evidence to show that these work, but some people find them helpful.(2) These natural chemicals, for example tea tree oil, can also cause side-effects, such as scalp irritation.(3) The use of "suffocating agents", such as food oils, hair gels and thick creams, to smother the lice on the scalp are increasing in popularity. It is felt that these agents cause the head lice to lose their grip on the slippery hair, and also probably block the breathing apparatus (spiracle) of the louse.(5) There are only anecdotal reports on the success of this treatment.(6)
In my department we use Dermol 500 Lotion (Diomed) and Epaderm (Medlock) on infected scalps where there is scratch damage and crusting. Dermol 500 lotion has the antimicrobial properties that help to reduce infection, cleanse the skin and remove any loose scale or debris. Epaderm has a much thicker consistency and is rubbed into the scalp to help to gently remove the crust from the scalp and coat the hair for the bug-busting process. Both of these products can be left on the scalp overnight and washed out in the morning.
There are a number of new products on the market to treat head lice. There are electronic combs, which kill head lice when they come into contact with their teeth.  Hedrin lotion (Dimeticone; Thornton & Ross) is not like conventional insecticides, which rely on a toxic action to kill head lice, but instead kills the head lice with a nonchemical action. Dimeticone coats the head lice like a shrink-wrap, which kills them. It can be used again and again as Hedrin's mode of action means that lice do not develop resistance to it.

There is no set method of preventing head lice. Bug busting children's hair every week will help to detect lice and enable treatment to start quickly and reduce the risk of passing them on to others.


  1. British Association of Dermatologists. Head lice. Available from:
  2. Bupa. Head lice. Available from:
  3. PRODIGY. Head lice and nits. Available from:
  4. Ashton R, Leppard B. Differential diagnosis in dermatology. 3rd ed. Oxford: Radcliffe Publishing; 2005.
  5. Medinfo. Head lice. Available from:
  6. Harvard School of Public Health. Head lice: information and frequently asked questions. Available from: