Infrared radiation alleviates damage to epidermal melanocytes induced by ultraviolet irradiation: potential for improving the efficacy of phototherapy for vitiligo lesions.

Ultraviolet (UV) phototherapy has long been considered an effective method for treating skin pigmentary disorders. However, the efficacy of phototherapy is significantly lower than surgical approaches. This might be due to cell death caused by ultraviolet irradiation. This finding contradicts the common understanding of the role of ultraviolet irradiation in promoting the proliferation and migration of melanocytes and improving the efficacy of phototherapy in the treatment of pigmentary disorders, e.g., vitiligo, is an urgent task. In this study, we investigated the combinatorial effect of infrared (IR) radiation and UV irradiation on human epidermal melanocytes. Changes in gene expression were investigated by transcriptomic analysis, and the related mechanisms were analyzed. We discovered that IR protects epidermal melanocytes against cell death induced by UV irradiation and provides the benefit of enhanced melanin synthesis when combined with UV irradiation. We then evaluated the protective effect of IR against DNA damage and its effect on melanocyte proliferation. The results indicated that IR radiation could promote melanocyte proliferation while maintaining the melanin biosynthesis-promoting effect induced by ultraviolet irradiation. This is particularly useful for the treatment of vitiligo as it protects melanocytes against cell death while improving melanin synthesis, which could contribute to the repigmentation of vitiligo lesions. In conclusion, this study has shown that IR potentially protects normal melanocytes against damage induced by ultraviolet irradiation while enhancing the effect of ultraviolet irradiation on promoting melanin biosynthesis.