Interaction of Solar Radiation with the Human Skin

The solar radiation has multiple sub-components of which the ultraviolet radiation is the most potent and well-studied to cause cutaneous photocarcinogenesis. For a very long time, UVB was considered the main agent for solar-induced skin cancers through direct DNA damage; however, more recently, UVA has also been established to contribute to the process of carcinogenesis, notably by the formation of ‘dark’ CPDs. Both components contribute to pigment darkening on sun exposure. Other lesser energetic parts of sunlight, such as the visible light spectrum, have recently come into focus for their ability to generate photopigmentation, acting mainly through free radical generation, and mainly from the blue end of the spectrum, called high energy visible light (HEVL). Interestingly, the photopigmentation effects of visible light have been noted to be more significant and more persistent in SOC compared to higher skin types. This chapter addresses the contributions of each of these components towards the total impact of sun exposure on skin, with a specific emphasis on SOC and the differential outcomes noted in the group.