Knowledge of the histopathology of melasma is a prerequisite for understanding its pathogenesis. However, the histopathological characteristics of male melasma are not well characterized.

We sought to investigate the histopathological characteristics of melasma in men compared with those of women with melasma and solar lentigo.

Biopsy specimens were obtained from both the lesional skin and the adjacent nonlesional skin in 8 men with melasma, 10 women with melasma, and 5 men and women each with solar lentigo. The samples were stained using Fontana-Masson and Verhoeff-van Gieson. Immunohistochemistry for melanocytes, the estrogen receptor, progesterone receptor, factor VIIIa–related antigen, stem cell factor, and c-kit was performed.

Increased vascularity was found in the lesion of male melasma. The lesion to nonlesion ratio of the vessel area was increased in male melasma compared with lentigo groups. In the lesion of male melasma, there was a significant increase of stem cell factor and c-kit expression. In addition, the lesion to nonlesion ratio of stem cell factor was increased in male melasma compared with female melasma and lentigo groups. The lesion to nonlesion ratio of c-kit was also increased in male melasma compared with lentigo groups.

This study did not include clinical data regarding social habits and was not confirmed by other molecular techniques.

The results suggest that chronic ultraviolet radiation associated with signaling of paracrine cytokines plays an important role in the mechanism associated with hyperpigmentation in male melasma.