A head louse is a tan or greyish insect about the size of a strawberry seed. It feeds on human blood that it extracts from the scalp. The female louse produces a sticky substance that adheres each egg to a hair shaft. An egg is attached approximately 3/16 inch (4 millimeters) from the base of the shaft — an environment that provides an ideal temperature for incubating the egg.

The louse life cycle

A louse egg hatches after eight or nine days. What emerges is an immature form of the louse called a nymph. The nymph becomes a mature adult louse after nine to 12 days, and an adult lives for three to four weeks.

Transmission

Head lice crawl, but they cannot jump or fly. Most often transmission of a head louse from one person to another is by direct contact. Therefore, transmission is most often within a family or among children who have close contact at school or play.

There's some evidence that brushing dry hair with static electricity may make a louse airborne for a short distance.

Indirect transmission is not likely, but lice may spread from one person to another by items such as:

  • Hats and scarves
  • Brushes and combs
  • Hair accessories
  • Headphones
  • Pillows
  • Upholstery
  • Towels

Indirect transfer also could occur among items of clothing stored together. For example, hats or scarves hung on the same hook or stored in the same school locker could serve as vehicles for transmitting lice.

Jun. 18, 2014

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