Excessive sun exposure can also cause cataracts and diseases aggravated by UVR-induced immunosuppression such as reactivation of some latent viruses. Both forms can damage collagen fibers, destroy vitamin A in skin, accelerate aging of the skin, and increase the risk of skin cancers. Sunburn is caused by too much UVB radiation this form also leads to direct DNA damage and promotes various skin cancers. UVA radiation (95–97% of the UVR that reaches Earth’s surface) penetrates deeply into the skin, where it can contribute to skin cancer indirectly via generation of DNA-damaging molecules such as hydroxyl and oxygen radicals. Most public health messages of the past century have focused on the hazards of too much sun exposure. Today’s scientists have come to a similarly dichotomous recognition that exposure to the ultraviolet radiation (UVR) in sunlight has both beneficial and deleterious effects on human health. For the ancient Greeks and Romans, Apollo was the god of medicine and healing as well as of sun and light-but Apollo could bring sickness as well as cure. Each day, Apollo’s fiery chariot makes its way across the sky, bringing life-giving light to the planet.

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