Major Influencing Factors

Genetic Factors

Genetic component is the most important risk factor for melasma. However, no Mendelian pattern of segregation has been identified [9]. A case of melasma occurring in both identical twins was reported in England in 1987. It was triggered by hormonal stimulation, which worsened after sun exposure. Nevertheless, it did not occur in their other sister (not twin), which strengthens the hypothesis of genetic susceptibility to the development of melasma [10].

Several studies have attempted to recognize the prevalence of melasma in the general population. The reported prevalence of melasma ranges from 8.8 % in Hispanic female population in the Southern United States to as high as 40 % in Southeast Asian populations [11, 12]. In a self-administered questionnaire study that included 324 women, 48 % of patients with melasma had a family history of melasma (97 % in a first-degree relative). There was a low family history of melasma in patients with skin type I or II (34 %) compared with those in patients with skin types III to VI (57 %). Individuals with family history of melasma tended to have darker skin (90 % types III-VI) compared with those without family history (77 % types III-VI) [3].

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