Crabs, or pubic lice, are tiny, barely visible parasites (scientific name Pthirus pubis ) that live in the pubic area and cause itching. ("Lice" is plural. The singular is "louse.") Pubic lice are commonly called crabs because they are shorter and rounder than head and body lice , making them resemble crabs. They are usually found in the pubic hair but can also be found in other body areas with short hair (eg, eyelashes, eyebrows, armpits, mustache).

Crabs are parasites that can infect the human body. They are spread by personal contact, usually during sexual activity. They may also spread by sharing personal items, such as bedding, towels, and clothing, but this form of transmission is less common.

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors for crab lice include:

• Sexual contact with people who have crabs
• Contact with contaminated items, such as:
  • Bedding
  • Towels
  • Clothing
  • Toilet seats
  • Furniture

Symptoms include:

• Itchiness (can range from mild to severe)
• Tiny blue-gray bumps stuck to the skin called macula caerulea
• Skin breaks and possible bacterial infection (caused by scratching)

The doctor will ask about your symptoms and medical history. A physical exam will be performed. He or she will examine your pubic area for lice, lice eggs (called nits), and macula caerulea .

Treating crabs involves applying over-the-counter shampoo or cream rinse containing permethrin or pyrethrins. For resistant cases, topical malathion (a highly effective prescription medication approved only for patients older than 6 years) or lindane may be used.

Lindane, a second line treatment, should only be prescribed to patients who are unable to take other medications or who have not responded to them. According to the Food and Drug Administration’s warning, lindane can rarely cause serious side effects, including seizure and death. Those especially susceptible are infants, the elderly, children and adults weighing under 110 lbs, and individuals with other skin conditions. Lindane is a toxin and should not be overused. Patients are given small amounts (1-2 oz) of the shampoo or lotion and instructed to apply a very thin layer and not to reapply. For more information, visit the US Food and Drug Administration website.

Treatment steps:

• Wash the infested area and then towel dry.
• Thoroughly saturate hair with lice medication. If using permethrin or pyrethrins, leave medication on for 10 minutes. If using lindane, leave on for only four minutes.
• Thoroughly rinse off medication with water. Dry off with a clean towel.
• Following treatment, most lice eggs will still be attached to hair shafts. You can remove them with your fingernails or tweezers.
• Put on clean underwear and clothing after treatment.
• If you have lice in your eyebrows, you may be directed to coat your eyebrows thoroughly with petroleum jelly.
• To kill any lice and nits that may be left on clothing or bedding, wash those items used during the 2-3 days before treatment. Use the hot water cycle (130°F) of the washing machine. Use the hot cycle of the dryer for at least 20 minutes to dry clothes.
• Dry clean clothing that is not washable.
• Avoid sexual activity until partners have been treated.
• If necessary, treat again in 7-10 days.