The major clinical pattern in 50-80% of cases is the centrofacial pattern, which affects the forehead, nose, and upper lip, excluding the philtrum, cheeks, and chin.(1)
Multiple etiologies, including light exposure, hormonal influences, and family history, have been implicated in the pathogenesis of this disorder. Overall prevalence ranges widely at 1-50%, since values are typically calculated within a specific ethnic population within a geographic region.(1)
Hormonal influences play a significant role in the pathogenesis of melasma as seen by the increased prevalence with pregnancy, oral contraceptive use and other hormonal therapies.
Extra-facial melasma has also been associated with a peri-menopausal state.(1)
Morphologically, melasma presents as symmetric reticulated hyperpigmented patches with irregular borders on the centrofacial region, malar cheeks, mandible, and rarely upper chest and extremities.
UV light has been shown in clinical and laboratory studies to trigger and exacerbate the condition.
Historically, melasma has been classified as having three histologic variants: epidermal, dermal, and mixed.
In the epidermal type, there is increased pigment throughout the layers of the epidermis, particularly in the basal and suprabasal layers.
The dermal subtype presents melanin laden melanophages in the superficial and deep dermis.
Mixed melasma often displays combined histologic features of the epidermal and dermal subtype.(1)