Eruptive vellus hair cysts (EVHCs) refers to the typical presentation of vellus hair cysts as multiple lesions as opposed to the less commonly occurring solitary vellus hair cyst. EVHCs present as multiple, small (1-4 mm), skin-colored to hyperpigmented follicular papules on the chest and upper abdomen. They may also occur on the proximal extremities, including axillae and buttocks, and have been reported on the face, including eyelids, and genital areas. They are usually asymptomatic but may be pruritic. They may become inflamed, and occasionally transepidermal elimination of cyst contents may occur.

The etiology of EVHCs is unknown. It is thought that a developmental anomaly predisposes to follicular occlusion of vellus hairs, leading to subsequent cystic dilatation of the affected follicle. EVHCs generally occur sporadically but may be inherited in an autosomal dominant fashion or associated with a number of other disorders, including steatocystoma multiplex, trichostasis spinulosa, anhidrotic ectodermal dysplasia, pachyonychia congenita, Lowe syndrome and other neurological disorders, and chronic renal failure. An occurrence of forehead lesions has been reported with use of minoxidil 3% applied to the scalp.

EVHCs characteristically present from childhood through adolescence into early adulthood. Some cases have been reported in elderly patients. Familial cases appear to have an earlier age of onset, with some lesions noted in infancy and even at birth. No predilection in any race / ethnicity or sex has been established.