Riehl's melanosis involves

Riehl observed in 1917, observed patients with facial hyperpigmentation, most pronounced on the forehead and in the zygomatic and/or temporal regions is the dominant symptom. The cause was not found. Riehl's melanosis is today almost synonymous with pigmented contact dermatitis of the face. The commonest cause has been sensitizing chemicals in cosmetics. Riehl melanosis is a nonpruritic pigmented dermatosis characterized by brownish-grey facial pigmentation and is almost synonymous with pigmented contact dermatitis of the face, the most common causes of which are sensitizing chemicals in cosmetics. It produces a type IV cytolytic reaction at the epidermal basal layer Ref Harrison 20th edition pg 1233