Unveiling the mystery of Riehl's melanosis: An update from pathogenesis, diagnosis to treatment.

Riehl's melanosis is a hyperpigmentation disorder that has a significant psychological and social impact on individuals. In the past 10 years, new categories have been developed, raising questions about how to classify Riehl's melanosis. The mechanism of this disease remains unclear, although the type IV hypersensitivity response caused by allergic sensitization, as well as genetic, ultraviolet radiation, and autoimmune factors, is to blame. Clinical manifestation, dermoscopy, reflectance confocal microscopy, patch/photopatch testing, histopathology, and a novel multimodality skin imaging system have been used for the diagnosis. A variety of therapies including topical skin-lightening agents, oral tranexamic acid, glycyrrhizin compound, chemical peels, and lasers and light therapies (intense pulsed light, 1064-nm Q-Switched Nd: YAG laser, 755-nm PicoWay laser, nonablative 1927-nm fractional thulium fiber laser, new pulsed-type microneedling radiofrequency), with improved effectiveness. The latest findings on possible biomarkers and their relationship to other autoimmune diseases were also summarized.