How head lice are caught
- Lice are genetically programmed to move from one head to another. They want to meet different lice (not their brothers and sisters on the same head) and breed with them. Lice cannot jump, hop, fly or swim, but have several ways of moving onto another person (Lancet 2003;361:99–100).
- The most common method is to grab onto another person’s hair during head-to-head contact. They grab the hair with one leg and then climb onto it.
- If they are in danger (if you agitate the hair), they may go to the end of the hair and drop off, hoping to land somewhere better.
- Head lice can live for 3 days away from the head, and eggs can survive for 5 days. Therefore they could be spread by shared hats or helmets, combs, brushes, earphones or bedding. (Experts used to think this was unlikely, but have now changed their minds.)
Who gets head lice?
People of all ages can be infected by head lice. They are most common in children aged 4–11 (especially girls), probably because children have more head-to-head contact than adults. At this age, about 8% of children have head lice. Some people blame modern schooling, where young children are grouped around tables, instead of sitting at separate desks. Other people, such as grandparents, can then become infected. Outbreaks of head lice have occurred in residential care homes for the elderly, probably brought in by a child visitor.
More information can be found in our sections on how to tell if you have head lice and how to treat head lice, or read Dr Phil Hammond's light-hearted poem on head lice. If your scalp is itching, but you don't think you have head lice, see our pages on dandruff and itching.
Written by: Dr Margaret Stearn
Edited by: Dr Margaret Stearn
Last updated: Monday, March 7th 2011
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In the UK, each month 20% of hairdressing salons see head lice in a client's hair
An estimated 5% of the UK population has head lice
Each year in the UK, the NHS and the general public together spend £29 million on head lice treatments
'Lousy', 'nitwit', 'nit-picking', 'nitty-gritty', 'go through something with a fine-tooth comb' - all these phrases come from lice
The average person with head lice has about 20 lice. During their 30-day life, 20 lice will lay 2652 eggs (Lancet 2003;361:99-100)
After mating, a female head louse keeps spare sperm in a special container in her body (spermatotheca), so that she does not have to bother with mating again, but can use the sperm she has kept (Lancet 2003;361:99-100)
Head lice are fairly speedy. They can move at 23 cm per minute (Lancet 2003;361:99-100)
Head lice have probably been annoying humans for at least 72 000 years (New Scientist 2003;23 Aug)