This summary discusses adult patients. Scabies in children is addressed separately.

Scabies is an intensely pruritic eruption caused by the mite Sarcoptes scabiei var. hominis. It is transmitted most often via direct person-to-person contact and less frequently by fomites. It is extremely contagious, spreading between individuals who share close contact or living spaces. Prevalence rates are higher in children, residents of long-term care facilities, and sexually active persons, although scabies can appear in individuals of all ages and socioeconomic groups. Factors that contribute to the persistence and spread of scabies are overcrowding, delays in diagnosis, and poor public health awareness. Outbreaks in health care facilities, such as nursing homes, can result in dozens of patients and staff becoming infected.

In a typical infestation, there are 10-20 mites. Most patients mount an intense hypersensitivity reaction to the mites, which burrow into and just below the stratum corneum of the epidermis. This results in a widespread and highly pruritic eruption. The hypersensitivity reaction usually develops 2-6 weeks after initial infestation. Without medical treatment, the condition persists because the mites lay eggs, causing continued infestation. Scabies can cause a generalized eruption resembling erythroderma in the elderly, the institutionalized, and patients with immunosuppression or neurologic dysfunction (crusted scabies). In these patients, the mite burden is much higher, with thousands to millions of mites present on affected skin.