A parasitic infestation of the skin caused by a mite whose penetration is visible as papules, vesicles or tiny linear burrows containing the mites and their eggs. Lesions are prominent around finger webs, anterior surfaces of wrists and elbows, anterior axillary folds, belt line, thighs and external genitalia in men; nipples, abdomen and the lower portion of the buttocks are frequently affected in women. In infants, the head, neck, palms and soles may be involved; these areas are usually spared in older individuals. Itching is intense, especially at night, but complications are limited to lesions secondarily infected by scratching. In immunodeficient individuals and in senile patients, infestation often appears as a generalized dermatitis more widely distributed than the burrows, with extensive scaling and sometimes vesiculation and crusting (“Norwegian” or “crusted” scabies); the usual severe itching may be reduced or absent. When scabies is complicated by beta-hemolytic streptococcal infection, there is a risk of acute glomerulonephritis.

Diagnosis may be established by recovery from a burrow and microscopic identification of the mite, eggs, or mite feces (scybala). Care should be taken to choose lesions for scraping or biopsy that have not been excoriated by repeated scratching. Prior application of mineral oil facilitates collecting the scrapings and examining them under a cover slip. Applying ink to the skin and then washing it off will disclose the burrows.