Crabs are not dangerous. The main symptoms are itching, particularly at night, and reddish-brown flakes (of dried blood) in the underwear.
You get crabs by sexual contact, sleeping in the same bed, or by sharing clothes and towels with someone who has crabs. Since crabs and nits can survive off the body, you don’t need direct physical contact with another person to catch them (e.g. you can catch them from toilet seats and saunas).
You can get rid of crabs with shampoos or lotions (such as Kwellada or NIX) available in drug stores without a prescription. The shampoo is easier to use than the lotion, but some doctors believe the lotion is more effective. Before using these shampoos or lotions, be sure to read the instructions carefully. A single application is usually enough. If you feel the treatment did not work, do not repeat it before seven to 10 days; and consider seeing your doctor before a second treatment.
Some treatments for crabs contain a chemical called lindane, which may be toxic if large amounts are absorbed into your body. A single application should not be a problem, but if numerous applications are necessary, you may risk damaging your nervous system. A safe non-lindane alternative is permethrin (NIX).
You must also clean any clothes, bed sheets or towels that you have used in the past few weeks, in hot soapy water and a hot dryer. Your sexual partners and people you sleep with should follow the same procedures.