Riehl Melanosis

Riehl melanosis is an acquired pigmentary disorder that predominantly affects darker-skinned individuals, particularly older women. This condition is characterized by brown-gray reticulated-to-diffuse hyperpigmented macules or patches on the face, neck, and upper chest (see  Clinical Photographs of Riehl Melanosis). The etiology is presumed to be a type IV hypersensitivity reaction triggered by contact allergens such as personal fragrances, textiles, and cosmetics. However, genetic factors, autoimmune conditions, and UV light exposure may also contribute to the condition's development. Despite the distinctive clinical presentation of Riehl melanosis, a thorough evaluation is necessary for its differential diagnosis, which may involve various techniques such as skin biopsy, patch testing, dermoscopy, reflectance confocal microscopy, or newer diagnostic tools following an initial clinical examination of the patients. These tools are crucial for diagnosing and distinguishing Riehl melanosis from other differential diagnoses, including conditions such as lichen planus pigmentosus and erythema dyschromicum perstans, all falling under the spectrum of acquired dermal macular hyperpigmentation. Histopathological examination of a skin biopsy will reveal basal layer vacuolar degeneration accompanied by colloid bodies and pigment incontinence.  Apart from allergen avoidance, management of this condition involves sun protection and various tailored regular skincare measures. Treatment options include topical therapies (such as hydroquinone, azelaic acid, and retinoids), oral therapies (such as tranexamic acid, glycyrrhizin, and mycophenolate mofetil), chemical peels (such as salicylic acid and glycolic acid), and lasers and light therapy (such as 1064-nm quality-switched neodymium-doped yttrium aluminum garnet laser and intense pulsed light) to meet individual patient needs. Regular monitoring using the dermal pigmentation area and severity index (DPASI) is necessary to gauge treatment efficacy and mitigate potential psychosocial impacts. This involves ensuring regular observation for improvement of hyperpigmentation, which can have deleterious effects if left untreated, particularly in patients with Riehl melanosis. Riehl melanosis was first described by Gustav Riehl in 1917, who observed striking rough, indurated brown-gray pigmentation on the forehead, temporal, and zygomatic regions on patients' faces (see Riehl Melanosis on the Left Cheek). Initially, it was believed to be related to nutritional substitutions resulting from wartime food measures, such as poor-quality flour. However, it later became evident that it was also present on the faces of women who used cosmetic products. Consequently, the condition transitioned from being termed war dermatosis to melanosis faciei feminae, eventually becoming known simply as Riehl melanosis.  Riehl melanosis belongs to a group of conditions collectively referred to as acquired dermal macular hyperpigmentation (previously known as macular pigmentation of uncertain etiology). This group may encompass Riehl melanosis, erythema dyschromicum perstans, lichen planus pigmentosus, melasma, exogenous ochronosis, idiopathic macular eruptive pigmentation, and pigmented contact dermatitis. The acquired dermal macular pigmentation disorders have similar clinical and histopathological findings.  Pigmented contact dermatitis is considered a variant of Riehl melanosis, with an identified contact allergen, such as cosmetics like kumkum (see  Kumkum-Induced Pigmented Contact Dermatitis). Although pigmented contact dermatitis shares similarities with Riehl melanosis, the extent of inflammation observed creates distinctions between them. Some experts consider pigmented contact dermatitis and Riehl melanosis identical; however, this view may be controversial, as pigmented contact dermatitis typically exhibits minimal to no inflammation compared to Riehl melanosis. Thus, this group of conditions may be classified as acquired dermal macular pigmentation with or without contact sensitization. Please see StatPearls' companion resource, "Contact Dermatitis," for further information.