Pubic lice are wingless parasites (Pthirus pubis) that must have a human host to survive. They prefer to cling to the coarse hairs of the pubic region or any other location on body with this type of hair (e.g., eyebrows, eyelashes, armpits, legs, facial hair). They feed on human blood, and the human body is their sole host. Pubic lice are not carried or spread by animals.

Pubic lice are transmitted primarily through sexual contact. For this reason, a pubic lice infestation is considered a type of sexually transmitted disease or, more recently, a sexually transmitted infection (since carrying pubic lice is not technically a disease). Less often, they are passed from human to human via clothing, bedding and towels that are contaminated. While pubic lice do not carry disease (unlike body lice), people who have a pubic lice infestation may be at risk of contracting other sexually transmitted diseases.

Pubic lice are also known as “crabs” because they resemble crabs when viewed under a microscope. The bodies of pubic lice are shorter and rounder than those of head lice. Pubic lice are tan to grayish-white in color. Pubic lice are not able to fly. Their crablike claws allow them to cling to course hairs of the human body, but do not allow them to move easily about on smooth surfaces.

Adult females are slightly larger than adult males. After mating, the female lays eggs (called nits). One female can lay up to three nits per day over the course of about 10 days. These white or yellow oval-shaped nits are smaller than a grain of rice and can be difficult to see. Each nit is firmly attached to a coarse shaft of hair. Pubic lice hatch from nits about one week after being laid.

Newly hatched pubic lice (called nymphs) secure themselves to the base of a coarse shaft of hair and begin to feed on its human host. As pubic lice suck blood from their host, saliva and other irritating components are released, causing itchiness. Pubic lice also deposit black feces in the area. Nymphs mature into adult pubic lice in about seven days.

Pubic lice must consume human blood to survive. These lice can only live for 24 to 48 hours without a fresh intake of blood, such as when the lice become dislodged from their host.

A pubic lice infestation is extremely rare in infants and children. When infestation occurs, the lice may be found clinging to a child’s eyelashes or eyebrows. Pubic lice may cause inflammation of the eyelid (blepharitis) in children and adults, although pubic lice are not the only cause of this condition. Pubic lice in young children or prepubescent teens are usually spread from a parent who is infested (e.g., sharing contaminated bedding, clothes or towels), although they may indicate sexual activity or sexual abuse.

Skin redness and irritation due to scratching are common complications in people with pubic lice. In some cases, skin lesions may develop in the area. 

Pubic lice are one of three different kinds of lice that are human parasites. The other two are:

• Head lice. These lice infest hair on a person’s head. Head lice are common in children and outbreaks are common at school, daycare centers and other group settings where children have close contact with one another. Unlike pubic lice, head lice are not sexually transmitted.
  
  
• Body lice. Sometimes called bed lice, these lice are most common among unwashed, transient groups of people (e.g., homeless people). They live in the seams of unwashed clothing and bedding, and are the only human lice that can carry and spread disease (e.g., typhus). Body lice are also not sexually transmitted.