Vitamin D is primarily produced by a photochemical reaction in skin, using the energy of ultraviolet B radiation. Ultraviolet radiation in sunlight is also responsible for several types of DNA damage, immunosuppression and photoaging. A number of adaptive responses are known to occur in skin to increasing UV exposure, including increased pigmentation, increased thickness of the cornified layer of skin and upregulation of DNA repair pathways. In addition to these known responses, there is now sufficient evidence to suggest that the local vitamin D system in skin, which includes local production of the active hormone, 1,25 dihydroxyvitamin D, together with metabolites of over-irradiation products, and vitamin D receptor(s), also provide an adaptive response to UV. The vitamin D system in skin reduces DNA damage, inflammation and photocarcinogenesis. Because vitamin D is made in skin, sun damage is less than it would be otherwise.