Scabies is caused by the human itch mite, which is too tiny for most people to see with the naked eye. When one organism gets onto human skin it burrows into the top layer of dead skin and lays eggs. The eggs hatch in 5 days; those mites burrow in and produce more eggs. During this initial phase of reproduction, while a few hundred mites are produced, the human host experiences no itching or rash, but is contagious to others. Finally, after 2 or 3 weeks the human becomes allergic to the mites and an itchy rash develops. Paradoxically, only a dozen or so mites are now present, as the allergic response kills many of them.

The rash is usually extremely itchy, especially at night. Dozens to hundreds of tiny bumps are present all over the body, with greater concentrations in the fold areas, such as finger webs, wrist folds, armpits, belly button, under the breasts, and between the buttocks. There is often a rash on the nipples and genitals. Older children and adults almost never have rash above the neck and on the palms and soles, but infants frequently have rash at those sites. Some people have only a mild allergic reaction and develop only a few faint bumps with only mild itching.

Scabies are passed by skin-to-skin contact, usually among people sleeping together, and to children who are hugged and carried by adults. Casual contact such as handshaking or contact in crowds does not pass the organism. Mites live in the skin and do not come off easily, but occasionally an organism is shed into clothing or bedding where another human may contract it. Such passage is rare, partially because the organism can survive off a human host for only 12 to 24 hours (usually less).

Treatment of scabies is simple and effective. Children and adults apply a cream or lotion (prescribed by the doctor) to their entire skin surface below the neck. Do not apply just to rash or itchy areas, and do not skip the buttock folds, genitals, toe webs or other difficult treatment areas. The medication is applied at bedtime and washed off in the morning. One or two treatments are adequate, depending on the medication prescribed. Bed partners should be treated simultaneously. Infants may be given a different medication than that used by adults. They should be treated on the face and scalp as well as elsewhere.

Itching usually persists for a few days, or even a week or two, after treatment, because it takes time for the allergic reaction to subside. You doctor may prescribe creams or pills to relieve the itching. Do not increase your frequency of bathing or repeatedly use the anti-scabies cream because that further irritates the skin and can increase itching. If you think that you still have scabies or have re-acquired it you should return to the doctor for examination.

Simple precautions should be taken to prevent the spread of scabies in the home. First, all occupants who are in intimate contact with each other should be treated at the same time (whether or not they are itching). The morning after treatment the bed linen and nightclothes should be washed, as well as the clothes, which were worn the previous day. No other clothes or furnishings need be cleaned. Don't forget, scabies mites are rarely shed into the environment and survive less than 24 hours, so just setting aside clothing (which may be difficult to clean) for a day or two insures that it is safe to use again.