Sex hormones, such as estrogen and progesterone, are factors involved in the regulation of skin pigmentation . Melasma is more common in women, accounting for 90 % of all cases. It has been reported in 50-70 % of pregnant women as well as in 10-20 % of women using oral contraceptives [14, 15]. These clinical evidences suggest that estrogen may be more likely to trigger melasma.
In an in vitro cell culture model, estradiol has been shown to upregulate tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 transcription . Melanin synthesis is also increased by 17p-estradiol in human melanocytes in culture . In addition, estrogen receptor (ER)p expression showed an increasing tendency in the lesions compared with the unaffected area (mean ± standard deviation: 0.39 ± 0.17 vs. 0.31 ± 0.17, p > 0.05). The nuclear staining of progesterone receptor (PR) was also significantly increased in the lesions compared with the unaffected epidermis (0.47 ± 0.15 vs. 0.36 ± 0.14, p = 0.03) . Interestingly, an increased immunoreac- tivity of ERp was also noted in the dermis, especially around the small blood vessels and fibroblast-like cells compared with the unaffected dermis (1.33 ± 0.82 vs.
0.97 ± 0.59, p=0.04). However, there was no significant difference in the expression of PR between the lesions and the unaffected dermis (1.24 ± 0.90 vs. 0.96 ± 0.68, p = 0.17) . These results suggest that there may be an association between hormonal receptors and melasma.