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Causes of Head Lice

Head lice is directly caused by an infestation of the hair and scalp with a small, wingless insect called Pediculus humanus capitis. The causes of head lice have nothing to do with cleanliness or personal hygiene. Head-to-head contact is the most common form of transmission, but head lice can also be spread through contact with infested brushes, hats, or towels.

What Causes Head Lice?

The cause of head lice is an infestation with a parasitic insect known as Pediculus humanus capitis. This parasite is more commonly known as head lice -- so both the condition and the parasite that causes it go by the same name.

Understanding Head Lice

A head louse (head lice is plural) is a small, wingless insect. It has three pairs of legs located directly behind the head. The legs end in sharp claws that are designed for feeding and allow the louse to hold on tightly to hair or clothing. The head louse is the largest of the three types of lice (the pubic, or crab, louse is the smallest).
Head lice feed about five times a day. To feed, they pierce the skin with their sharp claws, injecting irritating saliva and then sucking the blood that flows. They do not become engorged, like ticks, but they do become rust-colored from the ingestion of blood. This rust color is an identifying characteristic of lice. Lice feces can be seen on the skin as rust-colored flecks.
A female louse lays about six eggs (also known as nits) each day. They reach maturity in about 18 days. Nits become firmly cemented at the base of the hair shaft, close to the skin, so that they stay warm. Nits are hard to remove from the hair shaft. The life cycle of head lice, from egg to adult, is approximately one month.

Risk Factors for Head Lice

Anyone who comes in close contact (especially head-to-head contact) with someone who already has head lice is at greatest risk. Occasionally, head lice may be acquired from contact with clothing (such as hats, scarves, and coats) or other personal items (such as brushes or towels) that belong to an infested person.
Preschool and elementary-age children (ages 3-11) and their families are infested most often. Girls get head lice more often than boys, and women get head lice more often than men.
In the United States, African Americans rarely get head lice.
Personal hygiene or cleanliness in the home or school has nothing to do with the causes of head lice -- this is a myth.
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About Head Lice

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