Head lice

Head lice

Head lice (Pediculus Capitis) are wingless insects that live on human scalps. They hatch around five to ten days after an egg is laid on a hair strand close to the scalp, leaving an empty shell (nit) firmly attached to the hair.

The young lice (nymphs) feed by piercing the skin of the host and sucking blood. When they pierce the skin they inject saliva containing anaesthetic and anticoagulant so that the host blood can be sucked freely without the host experiencing pain. Lice feed about six times a day.

Nymphs can change colour once after they have hatched to blend to the colour of the host’s hair, however if they move to another host they are unable to change colour again.

A nymph will become a full-grown louse after six days. Full-grown lice crawl from head to head (younger lice usually stay on the head where they hatch). Full-grown lice mate and the females start laying eggs- the earliest this happens is day seven after the female has hatched.

Female lice will lay around four eggs a day.

head louse

Lice do not survive long without a human host to feed from, and therefore the risk of contamination from towels, pillows or bedding for example is quite low.


There are a number of signs that indicate a head lice infection:

  • black powder on collars and pillows (which is faecal matter from the lice).
  • cast-off skins on combs, pillows, collars etc. (these look similar to lice).
  • dead or dying lice floating on the surface of water when the hair has been washed.
  • persistent itching of the scalp, caused by an allergic reaction to the head louse saliva. It may take two to three months for the itch to develop the first time a person is infected, although very young or older people can remain asymptomatic indefinitely.
  • the presence of tiny white empty egg shells (nits) attached to the hair. Note: Hair grows at about 1cm per month and therefore the distance the nit is from the scalp gives an indication of how long ago it was laid.


For detection a proper plastic detector comb must be used. Metal ones are unsuitable for detection as they miss small nymphs, cause damage to hair and are designed only for the removal of empty egg shells (nits).

wet combing


Wet combing is advised as the most natural, efficient and cost effective method to remove all lice. There are also various treatment lotions and sprays available through pharmacies or supermarkets, though please check the packet for suitability particularly if your child is under the age of 2 or if you are pregnant or breastfeeding.

The wet combing method:

  1. Wash the hair with ordinary shampoo and apply plenty of conditioner.
  2. Use an ordinary, wide-toothed comb to straighten and untangle the hair.
  3. Once the comb moves freely through the hair switch to a louse detection comb.
    [Combs with teeth spaced 0.2-0.3mm apart are best]
  4. Make sure the teeth of the comb slot into the hair at the roots, with the edge of the teeth lightly touching the scalp.
  5. Draw the comb down from the roots to the ends of the hair with every stroke, checking the comb for lice each time; remove the lice by wiping the comb with tissue paper or rinsing it between strokes.
  6. Work through the hair, section by section, so that the whole head of hair is combed through.

Remember that whatever treatment method, you should always check for (and remove) lice on days 5, 9 and 13 to avoid the risk of continuing infestation.

Note: Patients with asthma, eczema or psoriasis should not use an alcohol based lotion to treat head lice. The alcohol fumes may precipitate an asthma attack and the alcohol in the lotion may irritate sensitive or excoriated skin.


It is very difficult to prevent head lice. Preventative lotions, sprays, and the hot washing of bedding or towels are deemed unnecessary, as they are unlikely to prevent the spread of lice. The use of tea tree oil or coconut oil on the hair as a deterrent also remains widely contested.

Two of the main considerations involve:

  • Preventing the spread of lice from one head to another

Tying back hair or keeping it short and restricting hair-to-hair contact may help reduce the spread. However, detection combing is the best method to ensure your child is head lice free, and this may be done on a regular basis (once a month for example).

It is important to inform friends, family, work/school/nursery, or anyone you may have had close contact with if head lice have been found in your home. This can help accelerate the detection process, and ensure prompt treatment throughout the community.

The stigma of head lice will only lessen when people become more open about them.

  • Preventing head lice from reproducing

If someone is found to have lice in your house everyone should be checked, and treatment should be given to those with lice on the same day.

Take Part in a Bug Busting Day!

Bug Busting is carried out annually on January 31st, June 15th and October 31st; the days form part of a national education initiative, asking parents and schools to help take steps to eradicate head lice.

Parents (and carers) of young children are encouraged to check their heads for lice, regardless of itching or the sight of eggs. The aim is to identify and remove any lice in circulation, stopping the problem in one go and preventing endless circulation.

Schools (and nurseries) will inform parents when head lice have been detected on their premises, improving the likelihood of further cases being detected quickly. Schools also provide leaflets and further advice on how to treat head lice infestations twice a year (usually the first Friday of the week in February and again in October).