A common, contagious itching disease caused by Sarcoptes scabei hominis (see SARCOPTES) which can live only on human skin. The fertilised female burrows into the skin surface, creating a tunnel within it. The mites deposit 2–3 eggs per day each as well as faecal pellets, which contain the ALLERGEN which initiates an immune reaction responsible for symptoms. Eggs hatch within 3–4 days, producing larvae. After successive moults these become adult mites and the 15-day lifecycle re-starts. A rapid build-up of mite numbers is not noticed by the host until an immune response induces itching after about six weeks. Scabies is spread by skin-to-skin contact, usually via the hands, generally within a family or amongst sexual partners.

It results in severe itching, worse when the body is warm after a bath or in bed. Burrows are visible as wavy black lines 3–5 mm long in the skin of the hands, wrists or sides of the feet. PAPULEs, PUSTULEs, crusts and scratches may be seen on the hands and there may be a widespread eczematous (see DERMATITIS) or urticarial (see URTICARIA) rash elsewhere. Papules or nodules on the PENIS and SCROTUM are characteristic. In infants, burrows occur on the palms and soles. Rarely, absence of an immune response causes a mite-saturated, generalised scaly dermatitis (Norwegian scabies).