Pubic lice (Phthirus pubis) are ecto-parasitic insects that live in the course hair of the body. They are also known as Pediculosis pubis or by the common name “crab lice”. They are a parasite only of humans with no animals acting as an alternative host.
Most commonly, pubic lice inhabit the hair around the genital region. They can sometimes be found on other body hair, facial hair and even eyelashes. Where large numbers of lice occur, the condition is known as an infestation.
An adult louse is yellow/gray in color and about two millimeters long. The rear pair of its six legs are thicker than the others. They resemble the claws of a crab, which is where it gets its common name of “crab louse”. It uses these modified legs to grasp the thick hairs in which it lives.
They are blood-sucking insects and need to remain on their host for most of the time in order to survive. However, they can live for about 24 hours away from the body of their host. This allows them to change hosts via shared towels, bedding or underwear.
The most common way for pubic lice to be passed from one host to another is through close sexual contact. If someone has the lice infecting the beard or chest hair then hugging or kissing may allow the lice to change hosts. While pubic lice can be found on anyone of any age, they are most common in young sexually active adults.
An adult female louse will lay small eggs, which they affix to the base of a hair. The eggs hatch after about 6-10 days. During her lifetime, of 1-3 months, a female louse can lay up to 300 eggs. When the eggs hatch the white egg cases remain attached to the hair, these are known as nits.
Treatment of pubic lice requires the use of lotions containing an appropriate insecticide. With all treatments, the manufacturer’s directions should be followed unless otherwise directed by a doctor. The wet hair combing method, sometimes used for the removal of head lice, is not recommended for treatment of pubic lice.
There are two recommended insecticides used for the treatment of pubic lice. These are Malathion (0.5% aqueous lotion) and Permethrin (5% dermal cream). As the lice may not be obvious on other parts of the body, all body and facial hair except the eyelashes should be treated with these preparations. With Malathion, the area should be coated with the solution and left for 12 hours before washing. Permethrin should be applied and left for 24 hours before washing. A second treatment, seven days after the first, will ensure the removal of all lice within their life cycle. Permethrin is not recommended for use by persons under the age of 18, pregnant or breast feeding women.
If eyelashes need to be treated then a solution of 1% Permethrin is normally recommended. It should be carefully applied using a cotton bud and then left for 5-10 minutes before rinsing thoroughly with water. Treatment should be repeated at seven-day intervals. Some doctors may prescribe an eye ointment specifically for treating lice found on eyelashes.