Pubic lice are small, six-legged creatures that infect the pubic (genital) hair area and lay eggs. These lice can also be found in armpit hair and eyebrows.

Pubic lice are known scientifically as Phthirus pubis. Lice infestation is a common sexually-transmitted condition and is found mostly in adolescents. Transmission generally occurs during sexual activity, but it can occur through physical contact with contaminated objects such as toilet seats, sheets, and blankets. Some women have acquired it while trying on swimming suits at a store.

The presence of pubic lice is heralded by moderate to severe itching in the area covered by pubic hair. This itch is frequently worse at night. Because the crab louse requires human blood to survive, it buries its head inside a pubic hair follicle. It excretes a substance into the skin that causes the itching.

Sometimes the bite can cause an inflammatory skin reaction that is bluish gray in color. Although the lice do not cause a rash, the constant scratching and digging can cause the skin to become raw, and secondary infections may develop.

On close inspection, adult lice (1.2 mm in diameter) may be seen. A magnifying glass makes the lice more easily visible, and will show the small egg sacs or "nits" that are attached to the pubic hairs, usually at the base. In many cases, adult lice may only be seen in the seams of clothing.

Although pubic lice appear to prefer the pubic area, they can also thrive on the eyelashes. In young children, pubic lice may be a cause of blepharitis (an eye infection) and their eyelashes should be examined with a high-powered magnifying glass for evidence of lice.

In addition to pubic lice, there is body lice (Pediculus humanus corporis) and head lice (Pediculus humanus capitis).

Risk factors include:

• Being a sexually-active adolescent
• Having multiple sexual partners
• Having sexual contact with an infected person
• Sharing bedding or clothing with an infected person

• Itching in pubic hair region
• Eggs (nits) or actual adult lice may be seen
• Genital lesions due to bites
• Other genital lesions consisting of scratched areas and possibly secondary infections

An examination of the external genital region typically reveals small gray-white oval eggs (nits) attached to the hair shaft and may reveal adult lice. Scratch marks or signs of secondary infection such as impetigo may also be noted.

Adult lice may be easily identified under the microscope. Their crab-like appearance is the reason that pubic lice are referred to as "the crabs."