riehl melanosis riehl melanosis riehl melanosis is a form of contact dermatitis, beginning with pruritus, erythema, and pigmentation that gradually spreads which, after reaching a certain extent, becomes stationary.: 857 the pathogenesis of riehl melanosis is believed to be sun exposure following the use of some perfumes or creams (a photocontact dermatitis).: 858 riehl melanosisspecialtydermatology riehl melanosis is named after the dermatologist gustav riehl, who first described the condition in 1917.