Scabies, also known as sarcoptic itch and acariasis, is the highly contagious infestation with Sarcoptes scabiei, a tiny, whitish-brown, eight-legged mite that burrows into the skin to lay its eggs. Burrowing, egg laying, and feces deposition cause severe skin irritation, eruption, and itchy rash. Scabies is a fairly common disease caused by a very tiny mite that lives in, or just below, the surface of human skin. It can be spread among people of all races, incomes, ages and levels of
cleanliness. The female scabies mite lays her eggs in burrows or channels just beneath the skin. Young mites develop in a few days and emerge from the burrows. Proper applications of a scabies treatment product kills adult mites and eggs; however, a person can get scabies again if he or she is re-exposed to the scabies mite.
Scabies is caused by a small insect or mite known as S. scabiei var. hominis. This mite is about the size of a pinhead and can live only 24 hours at room temperature apart from the human body. It burrows into the outer layer of skin and lays eggs, which hatch in 3-5 days. After hatching, the newly formed mites leave the burrow and move to other skin surfaces and repeat the cycle. Scabies is not caused by being dirty. Scabies mites are very fastidious. They need a warm body and can't live without one for more than an hour or so. That is why transmitting them requires prolonged physical contact of the skin-to- skin variety. It is hard, if not impossible, to catch scabies by shaking hands, hanging your coat next to someone who has it, or even sharing bedclothes that had mites in them the night before. The physical contact required to contract scabies may of course be sexual, and scabies is more common among sexually active young people. However, other forms of physical contact, such as mothers hugging their children, is sufficient to spread the mites. Over time, close friends and relatives can contract it this way too. For this reason, scabies is not considered a sexually transmitted disease in the usual sense.
Scabies burrows are found between the fingers, around the wrists, armpits, buttocks, on the penis, insteps and backs of the heels. Itchy lumps on the penis are almost always due to scabies and they are also very suggestive if found on the buttocks or in the armpits (nodules). There may be pustules on the palms and soles, particularly in infants. Scabies only rarely affects the face and scalp. One may have scabies for several weeks before there is any itch or rash. During this time a patient can unknowingly pass it on to others. Then the rash appears with tiny red intensely itchy bumps on the limbs and trunk. It can easily be confused with dermatitis or hives. The itch and the rash of scabies is due to an allergy to the mites and their products. Norwegian scabies (crusted scabies) is a very contagious variant in which there is little itch but numerous mites. These cause a generalised scaly rash that may affect the scalp.
Skin lotions or creams containing lindane, permethrin, pyrethrin or crotamiton are applied to the skin of a person with scabies and to that of other individuals who have had skin-to-skin contact with that person. These treatment products are only available with a doctor's prescription. Instructions for their use vary from product to product, but treatment products should not be used more often than the doctor prescribes. It is always important for the physician to carefully select treatment products, but especially so for infants, young children and pregnant women. Scabies resistance to lindane has been reported in some areas of the world, including parts of the United States.
To properly treat and kill the scabies mites and eggs, it is necessary to apply the lotion or cream thoroughly to all areas of the body from the chin down to, and including, the soles of the feet. Because scabies can affect the scalp and head of infants and young toddlers, it is important to include these areas when treating the rest of the body of a person in this age group. Treatment of the person is repeated in seven days to get rid of any eggs that survive the first treatment. Itching often lasts for more than one week and can even last several weeks after effective treatment. Itching that continues does not mean the treatment has failed or that the person has gotten scabies again. It is important not to overuse treatment products.
It is uncommon for only one person in a family to have scabies. The ongoing physical contact that occurs in family settings easily spreads the scabies mite. Up to six weeks can pass before the itching, red bumps, blisters or rashes begin and during this time the mite can be spread among family members. Therefore, family members, sexual contacts and others who have had skin-to-skin contact with a person diagnosed with scabies also need to be treated as soon as the person is diagnosed.