Scabies (also known as the seven-year itch) is a contagious skin infestation by the mite Sarcoptes scabiei.[1][3] The most common symptoms are severe itchiness and a pimple-like rash.[2] Occasionally, tiny burrows may appear on the skin.[2] In a first-ever infection, the infected person will usually develop symptoms within two to six weeks.[2] During a second infection, symptoms may begin within 24 hours.[2] These symptoms can be present across most of the body or just certain areas such as the wrists, between fingers, or along the waistline.[2] The head may be affected, but this is typically only in young children.[2] The itch is often worse at night.[2] Scratching may cause skin breakdown and an additional bacterial infection in the skin.[2]

Scabies is caused by infection with the female mite Sarcoptes scabiei var. hominis, an ectoparasite.[3] The mites burrow into the skin to live and deposit eggs.[3] The symptoms of scabies are due to an allergic reaction to the mites.[2] Often, only between 10 and 15 mites are involved in an infection.[2] Scabies is most often spread during a relatively long period of direct skin contact with an infected person (at least 10 minutes) such as that which may occur during sex or living together.[3][9] Spread of the disease may occur even if the person has not developed symptoms yet.[10] Crowded living conditions, such as those found in child-care facilities, group homes, and prisons, increase the risk of spread.[3] Areas with a lack of access to water also have higher rates of disease.[4] Crusted scabies is a more severe form of the disease.[3] It typically only occurs in those with a poor immune system and people may have millions of mites, making them much more contagious.[3] In these cases, spread of infection may occur during brief contact or by contaminated objects.[3] The mite is very small and usually not directly visible.[3] Diagnosis is based on the signs and symptoms.[5]

A number of medications are available to treat those infected, including permethrin, crotamiton, and lindane creams and ivermectin pills.[7] Sexual contacts within the last month and people who live in the same house should also be treated at the same time.[10] Bedding and clothing used in the last three days should be washed in hot water and dried in a hot dryer.[10] As the mite does not live for more than three days away from human skin, more washing is not needed.[10] Symptoms may continue for two to four weeks following treatment.[10] If after this time symptoms continue, retreatment may be needed.[10]

Scabies is one of the three most common skin disorders in children, along with ringworm and bacterial skin infections.[11] As of 2015, it affects about 204 million people (2.8% of the world population).[8] It is equally common in both sexes.[12] The young and the old are more commonly affected.[5] It also occurs more commonly in the developing world and tropical climates.[5] The word scabies is from Latin: scabere, "to scratch".[13] Other animals do not spread human scabies.[3] Infection in other animals is typically caused by slightly different but related mites and is known as sarcoptic mange.[14]