Riehl Melanosis

Facial melanoses affecting the face and neck region are of considerable concern to darker-skinned people. Although many facial melanoses, such as melasma, are well defined clinically, rendering them easy to diagnose, others have overlapping clinical morphology as well as histopathology. Riehl melanosis (RM), commonly considered as a pigmented contact dermatitis (PCD), is one such condition with diverse yet overlapping clinical features with other facial melanoses as ashy dermatosis and lichen planus pigmentosus. Definition RM is best defined as an acquired low-grade allergic contact dermatitis to fragrance and other cosmetic products that presents with abnormal hyperpigmentation involving the face and neck regions. The disorder is known to predominantly affect patients of Asian descent. Historical Aspects of Nosology of Riehl Melanosis During the first world war, Riehl first identified several patients of both genders with striking dark brown to grayish-brown pigmentation on the forehead, temporal, and zygomatic regions of the face. The involved skin was mildly indurated with a rough texture and appeared to mildly scaly without any erythema or atrophy. The pigmentation was diffuse and uniform but without well-defined margins. It extended to the ears and neck, with gradual fading off towards the chest as small discreet pigmented follicular-based macules. Other body parts like the axillae, arms, and forearms, submammary and umbilical regions also showed similar pigmentation, but it was much lighter than the face. Riehl was uncertain about the etiology, but he suggested wartime food substitutes, mainly poor-quality flour, as being contributing factors. The condition seemed to have disappeared, with no cases reported towards the end of the war. Later, similar cases were described from different centers. Hoffmann and Habermann emphasized that local chemical irritation due to the use of certain oils and hydrocarbons were responsible for melanosis similar to Riehl melanosis and labeled it 'melanodermatitis toxica.' However, this entity was not accepted by Riehl. The term "Riehl melanosis" became popular in the period between the two World Wars for facial melanosis caused by external chemical agents. During the Second World War (1945-1948), 165 new cases of suspected RM were diagnosed in Vienna with a female predominance. This condition disappeared again with the end of the war. Since then, RM was reported from many centers across the globe, especially from France and Argentina. The inflammatory component of the early phase of RM was strongly suggested by Miescher and was confirmed on histology in 200 cases by Joulia et al. in 1950. The etiology of RM was unknown until the late 1940s and 1950s when two studies from Argentina by Pierin et al. and Puente et al. attributed facial pigmentation similar to RM to cosmetic ingredients, typically aniline dye (orange II) found in facial powder. Positive patch tests to the dye were supported by the disappearance of early inflammation and progressive reduction in pigmentation on discontinuing the use of the facial powder. In 1970, the term "pigmented contact dermatitis" was coined by Osmundsen, a Danish dermatologist who documented several cases of peculiar facial hyperpigmentation in Copenhagen. Investigation revealed that hyperpigmentation was the result of contact dermatitis to an optical whitener, Tinopal CH 3566, in washing powder. Subsequently, in 1973, the term pigmented cosmetic contact dermatitis was introduced by Nakayama, a Japanese dermatologist, for cases that were ascribed to cosmetic contact allergens especially Brilliant Lake Red R. To date, the etiology of RM is still controversial, although the majority of experts consider it synonymous with PCD of the face. However, a recent global consensus statement emphasized that finely reticulated hyperpigmentation on the face and neck region should be labeled “pigmented contact dermatitis” rather than RM if its appearance is preceded by contact allergy. If etiology is uncertain, the term RM should be used.