Lichen spinulosus is a rare and benign cutaneous disorder characterized by sudden onset of localized circumscribed plaques composed of follicular hyperkeratotic papules. It most frequently occurs in children and adolescents; however, young adults can also be affected. There is a slight male preponderance. Individuals of any race can be affected. The etiology and pathogenesis are not known, although atopic, infectious, and genetic factors have been proposed as causes. Patients often have a history of atopy. An actinic variant has been described in which patients suddenly worsen in the summer or present following acute prolonged ultraviolet (UV) exposure, such as attending outdoor sporting activities.

Although usually localized to certain sites of predilection, a more severe generalized variant of lichen spinulosus also exists. This variant occurs in association with nodulocystic acne and pityriasis rubra pilaris as part of type VI (HIV-associated) pityriasis rubra pilaris. Additional rare associations include Crohn disease, Hodgkin disease, seborrheic dermatitis, syphilis, id reactions to fungal infections, and heavy metal ingestions. Note that these associations are not causal relationships and may be the consequence of ascertainment bias.

Lichen spinulosus has a variable course. Most cases tend to resolve spontaneously at puberty; however, persistent cases have also been described. Although no treatment is required, effective therapeutic options include topical keratolytic agents and topical retinoids.