Lice are small, wingless parasitic insects that feed on a human's blood. They can be found on various parts of the body, depending on the type. They are most often spread through close contact with someone already infested or through sharing personal belongings.
When a person is infested (whether it is on the head, body, or pubic area), the condition is known as pediculosis.
The three kinds of lice that affect humans include:
Each type looks similar. They are very 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 in size; the crab louse is the smallest.
Infestations are very common today. However, there are no reliable data on how many people get lice in the United States each year. While anyone can get infested, it is more common in certain groups of people, depending on the type of lice. For example, children are more likely to get head lice, while homeless people are more likely to get body lice. Pubic lice are more common in adolescents who are sexually active or in people with multiple sex partners.
One common myth is that personal hygiene or cleanliness in the home or school affects the chances that a person will get lice. This is not true for head lice or pubic lice. It is, however, true for body lice.
You can learn more about the specific causes for each type by clicking on any of the following links:
How Are They Transmitted?
Lice are very contagious. Direct contact with an already infested person is the most common way that
head lice and
pubic lice are spread.
Body lice are most often spread through contact with infected clothing or bedding. Pubic lice and body lice can also be spread this way, but it is less common than direct contact.
The insects are quite active and can travel quickly, which explains why they are transmitted so easily. However, they are not long-distance travelers, and they do not do well away from the host. Although adept at moving from hair to hair, they cannot jump or crawl very far (from the floor to someone's head, for example).
(Click any of the links below for more information on how each type is spread:
(Click Lice Prevention to learn how to prevent any of these types of infestations.)
There are three stages of a louse's life:
- The egg (also called a nit)
- The nymph
- The adult.
The life cycle from egg to egg is approximately one month.
The Nit
Nits are head lice eggs. They are very small (about the size of a knot in thread) and hard to see. Nits are often confused for dandruff or hair spray droplets. They are oval and usually yellow to white. They take about one week to hatch. Once hatched, they are white or clear in color.
Nymph
The nit hatches into a baby louse called a nymph. It looks like an adult louse, but is smaller. Nymphs mature into adults about seven days after hatching. To live, the nymph must feed on blood.
Adult Head Louse
The adult louse is about the size of a sesame seed, has six legs, and is tan to grayish-white. In people with dark hair, the adult louse will look darker. Female lice, which are usually larger than the males, lay eggs. To live, adult lice need to feed on blood. If a head louse or pubic louse falls off a person, it dies within two days.
Body lice can live up to 10 days without feeding.
The most common symptom with any of the types of lice is itching. This is because the saliva of the insects causes an allergic reaction. Keep in mind that not everyone will have symptoms.
Head lice can be anywhere on the scalp, but most commonly are seen behind the ears and on the back of the head near the neckline. When looking at the scalp, very few insects are usually seen. This is because they move very quickly. However, there are usually many nits (lice eggs) at the base of the scalp
(see Signs of Head Lice).
Pubic lice are generally found in the genital area on pubic hair, but may occasionally be found on other coarse body hair, such as hair on the legs, armpits, mustache, beard, eyebrows, or eyelashes. Infestations in young children are usually on the eyebrows or eyelashes
(see Signs of Pubic Lice).
The most common symptom of body lice is also frequent intense itching. Long-term infestations of the body may lead to thickening and discoloration of the skin, particularly around the waist, groin, and upper thighs
(see Signs of Body Lice).
Lice are diagnosed by looking closely at the affected area, whether it is the head, back of the neck, underarms, or genital area. The different types of lice do not usually affect other parts of the body. For example,
head lice do not affect the genital area, and
body lice do not affect the head.
(Click any of the following links for more information on how these conditions are diagnosed:
Treatment will vary based on the type of infestation a person is diagnosed with.
For example, to get rid of head lice you must do two things: kill the live insects on the head, and remove all the nits (head lice eggs) from the hair. This involves three necessary treatment steps:
On the other hand, getting rid of body lice may only require giving the infested person a clean change of clothes and a shower, and by laundering or throwing away all worn clothing, bed linens, and towels.
(Click any of the following links to learn about how the various types of infestations are treated:
