Review articleAn updated review of melasma pathogenesis

Melasma is a pigmentation disorder characterized by common clinical findings. However, the pathogenic mechanisms involved are heterogeneous in different individuals and ethnic groups. We have reviewed the pathophysiological mechanisms involved in melasma. Although the pathogenesis has not entirely been elucidated thus far, new findings are being identified by research groups. Epidemiologic studies may provide clues on the involvement of genetic factor(s), UV irradiation, or hormones in melasma. Some of the mechanisms of altered skin pigmentation, such as UV-induced pigmentation, may also be applicable to the pathogenesis of melasma. In fact, an increase in similar keratinocyte-derived melanogenic factors and their receptors occur in both UV-induced melanogenesis and melasma. Increased expression of female sex hormone receptors and the identification of the PDZ domain containing 1 (PDZK1) signaling mechanism provide insights to further our understanding of melasma. In addition to keratinocyte-derived paracrine factors, the role of paracrine factors from dermal fibroblasts, such as stem cell factor (SCF) and Wnt inhibitory factor-1 (WIF-1), is elucidated in melasma. Furthermore, the involvement of ion exchangers and microRNAs (miRNAs), such as H19 miRNA (miR-675), are also suggested.