Causes of Head Lice

Authored by Dr Mary Harding, 24 Aug 2016

Patient is a certified member of
The Information Standard

Reviewed by:
Dr Laurence Knott, 24 Aug 2016

Head lice are common in children but can affect anyone of any age. They are particularly common in primary school-age children.
  • Head lice are tiny grey/brown insects. They are about the size of a sesame seed (the seeds on burger buns). Head lice cling to hairs but stay close to the scalp which they feed off. Head lice lay eggs which hatch after 7 to 10 days. It takes about 7 to 10 days for a newly hatched louse to grow into an adult and start to lay eggs.
  • Nits are the empty yellow-white eggshells which are left when the lice hatch. Nits look like dandruff but stick strongly to hair. Unlike dandruff, you cannot easily brush out nits.

They are common all over the world.

They are not a sign of dirty hair or poor hygiene. Close hair-to-hair contact is usually needed to pass lice on. Head lice cannot jump or fly but walk from one head to another. They soon die when away from hair and they do not live for long in clothes, bedding, etc. However, they can occasionally be passed by sharing items such as brushes, combs, hats or bedding. Most head lice infections are caught from family or close friends who are not aware that they have head lice.

Head lice are more common in children with long hair and, partly for this reason, tend to be more common in girls. The more children there are in any one family, the more common head lice are.

Further reading and references

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