Pubic lice are small, wingless insects that live in a person’s pubic hair. They feed on blood, which can cause the person to itch. Their proper, scientific name is Phthirus pubis, but they are also called crab lice, or crabs. This is because, when looked at under a microscope, you can see that they have crab-like claws that they use to hold on to the shaft of the pubic hair. They can be seen with the naked eye, and have a flat body, which can grow to up to 2mm across. The females lay their eggs (nits) on the hair shaft, and they will usually hatch around 8 days later. They are usually transmitted by sexual contact, but they can also infect children (probably from transmission from a parent.) In children, they will often be seen to attach to eyelashes. They are unable to colonise scalp hair, as their claws are too big to hold onto the hair shaft; however, men may sometimes find lice in their facial hair.
A person will usually notice either the lice or the eggs, and will go to see the doctor or a GUM (genitourinary medicine) clinic. They may also have an itch caused by the bites. Treatment is use of an insecticide lotion that kills the lice, such as permethrin, phenothrin, or malathion. The person’s sexual partner(s) should also be treated, and the lotion should be reapplied 8 days later to get rid of the lice that have hatched from the eggs after the first treatment. The patient should also be advised to wash their clothes and bed sheets in hot water to kill any remaining lice.