Symptoms and causes

You may not be aware of a lice infestation. However, common signs and symptoms can include:

  • Itching. Itching on the scalp, neck and ears is the most common symptom. This is an allergic reaction to louse saliva. When a person has an infestation for the first time, itching may not occur for two to six weeks after infestation.
  • Lice on scalp. Lice may be visible but are difficult to spot because they're small, avoid light and move quickly.
  • Lice eggs (nits) on hair shafts. Nits stick to hair shafts. Incubating nits may be difficult to see because they're very tiny. They're easiest to spot around the ears and the hairline of the neck. Empty nits may be easier to spot because they're lighter in color and further from the scalp. However, the presence of nits doesn't necessarily indicate an active infestation.

When to see a doctor

See your doctor before you begin treatment if you suspect that you or your child has a head lice infestation. Studies show that many children have been treated for head lice with over-the-counter medications or home remedies when they don't have an active head lice infestation.

Things often mistaken for nits include:

  • Dead or empty nits from a previous head lice infestation
  • Dandruff
  • Residue from hair products
  • Bead of dead hair tissue on a hair shaft (hair cast)
  • Scab tissue, dirt or other debris
  • Other small insects found in the hair

A head louse is a tan or grayish 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.

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 could also 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.

Household pets, such as dogs and cats, don't play a role in spreading head lice.

Because head lice are spread primarily by head-to-head contact, the risk of transmission is greatest among younger people who play or go to school together. In the United States, cases of head lice most often occur in children in preschool through middle school.

If your child scratches an itchy scalp from a head lice infestation, it is possible for the skin to break and develop an infection.