Causes of Lice
Lice is caused by an infestation with one of three types of a small, wingless insect. The type of insect a person is infested with determines the type of lice the person has -- head lice, body lice, or pubic lice. Certain risk factors, such as sharing clothing or bedding with an infested person, can increase your likelihood of becoming infested.
The cause of lice (known medically as pediculosis) is an infestation with one of three types of a parasitic insect. The three kinds of lice that affect humans include:
- Pediculus humanus capitis (head lice)
- Pediculus humanus corporis (body lice)
- Phthirus pubis (pubic lice or crab lice; also called crabs).
Each type of lice looks similar. They are small (about 2 mm), flat, and wingless. They have three pairs of legs located directly behind the head. The legs end in sharp claws that are designed for feeding and allow for the louse to hold on tightly to hair or clothing. The head louse is the largest; the crab louse is the smallest.
To feed, lice pierce the skin with their sharp claws, injecting irritating saliva and sucking blood. 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 are active and can travel quickly, which explains why they are transmitted so easily. The lice life cycle from egg to adult is approximately one month.
(Click What Do Lice Look Like? to see pictures of the different types of lice, including their nits.)
Risk Factors for LiceAnyone who comes in close contact with someone who already has lice is at greatest risk. Occasionally, head lice or body lice may be acquired from contact with clothing (such as hats, scarves, coats, etc.) or other personal items (such as bedding or towels) that belong to an infested person. This is the more common mode of transmission for body lice.
Risk factors for pubic lice include:
- Having multiple sex partners
- Sharing clothing or bedding with an infested person
- Having sexual contact with an infested person
- Being a sexually active adolescent.
You can learn more about the specific lice causes for each type by clicking any of the following links: