What are head lice? 

Head lice are the most common of our mammalian parasites to infect humans and infest the hair and scalp. Epidemics often occur at the start of each school year. Head lice live on human blood and bite the skin a few times each day. Itching is the most common symptom of head lice infestation and is a consequence of the bites. Lice can neither fly nor jump; they crawl slowly from place to place. They are adapted to the body heat of the host and stay there since they cannot survive for more than twenty-four hours away from the human body. Head lice usually live for about one month. 

Neither a dirty environment nor poor hygiene is associated with head lice infestation since they feed on human blood, not dirt. Consequently, head lice do not spread either viral or bacterial infections, which is a common misunderstanding. Head lice infestation is not dangerous but may precipitate an epidemic since they readily spread. Head lice can affect anyone. 

The female is about 3 mm long, the male somewhat smaller. Lice are usually grayish yellow. Females lay about 200 eggs during their lifetime which they attach to hair strands close to the scalp. The eggs, which are also called nits, are oval and about 0.8 mm long. The eggs hatch within 6-9 days. The nymphs then develop over a period of 9-12 days before they become mature adult lice.

How do head lice spread?

Head lice prefer humans as a host and are therefore disinclined to leave the human body. Head lice are spread almost exclusively through direct head to head contact. They cannot survive for more than 24 hours if they are removed from the scalp. Hats, combs and hairbrushes may be a source of infection, but after only three to four hours away from the scalp, the lice weaken so much that they can no longer reproduce. In general, head lice do not spread via other objects that have come into contact with the hair and scalp, such as pillows or towels. 

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Page edited 2016-01-07.