Langerhans cell histiocytosis (LCH) is a systemic disease associated with the proliferation and accumulation (usually in granulomas) of Langerhans cells in various tissues.

An inflammatory process in skin caused by an exogenous agent that directly or indirectly injure the skin. If the offending agent is identified and removed, the eruption will resolve. An unusual or patterned eruption may be a clue to the presence of a contact dermatitis. Patch testing may be helpful in the differential diagnosis.