Sunlight is the most visible and obvious source of comfort in the environment. The sun provides the beneficial effects of warmth and vitamin D synthesis; however, acute and chronic sun exposure also have pathologic consequences. Few effects of sun exposure beyond those affecting the skin have been identified, but cutaneous exposure to sunlight is the major cause of human skin cancer and can exert immunosuppressive effects as well. The sun's energy reaching the earth's surface is limited to components of the ultraviolet (UV), the visible, and portions of the infrared spectra. .
