Eco-evolutionary impact of ultraviolet radiation (UVR) exposure on microorganisms, with a special focus on our skin microbiome.

Sunlight is pivotal for our survival, and daily UV exposure has impacted the evolutionary course of all forms of life, from microorganisms to humans. Deciphering the role of UVR in regulating the microbial dynamics of environmental and host-associated microbes is crucial. UVR may be responsible for affecting skin pathology by influencing the skin microbiome, both qualitatively and quantitatively, as evident in low-dose narrow-band UVB phototherapy. Some findings have suggested that the skin microbiome has immunomodulatory roles when exposed to UVR; however, its involvement in UV screening or protection has yet to be fully explored. Furthermore, numerous skin disorders are associated not only with an altered skin microbiome but also with an altered gut microbiome. Hence, the skin-gut axis needs to be in physiological homeostasis and immunological harmony. The purpose of this review is to examine the impact of natural UVR on human immunomodulatory mechanisms and the associated cutaneous microbiome, with an emphasis on interactions among UVR, skin homeostasis, vitamin D, and the related skin-gut axis. With the 'nature as an inspiration' approach, ongoing research is trying to decipher photoprotective secrets in several microbial-based natural compounds to be used as sunscreens or other topical formulations. In addition, various probiotics have also been shown to have significant antioxidant, antiwrinkle, and antiaging effects that ameliorate UV-induced cellular and molecular damage, as highlighted in the review. These cosmetics, nutricosmetics, and probiotaceuticals will undoubtedly be next-generation solutions against photoaging and maintaining skin health.