HERE COMES THE SUN: The sun emits three forms of light: infrared (heat), visible light, and ultraviolet (UV) light. It is the latter that is responsible for skin damage: prolonged exposure can damage and kill skin cells, which then release chemicals that activate the body's pain receptors. The energy from UV light also stimulates the production of a pigment known as melanin, which causes the skin to darken, or tan. Melanin actually absorbs the UV radiation in sunlight, protecting skin cells from further damage. Melanin is produced gradually, which is why would-be tanners must build up levels of the protective pigment in their skin cells over the course of several days. It's also why darker-skinned people are less likely to burn or suffer from skin cancer than those of fairer complexion: they possess naturally high levels of melanin. In contrast, albinos don't have any melanin at all in their skin, hair, or irises because they are missing a critical enzyme required for its production.
ABOUT THE UV INDEX: The UV index is a standard measure of the amount of UV radiation striking the Earth's surface, and the most accurate measure of sun exposure risk. In the US, the UV index starts to increase in March and April, peaking every year in June. The ozone layer in the Earth's upper stratosphere absorbs most of the sun's UV radiation, but ongoing damage to that protective layer means that UV-related health risks continue to increase.
SUNBURN: Sunburn occurs when skin cells are damaged by ultraviolet light. The body responds by increasing bloodflow to the capillaries in the dermis layer of the skin to repair the damage, and this extra blood causes the redness of sunburn. Melanocytes are also responsible for developing skin cancer, caused when the cells mutate after repeated exposure to ultraviolet light. Surface reflections can increase the effects of ultraviolet exposure. For example, snow reflects 90 percent of ultraviolet light, which is why you can get a sunburn while skiing on a sunny day. Sand reflects as much as 20 percent of ultraviolet rays, perhaps one reason some people tan faster at the beach. Glass, however, absorbs ultraviolet light; this is why we don't get sunburned while driving or working in a glassed-in greenhouse.
This report has been produced thanks to a generous grant from the Camille and Henry Dreyfus Foundation, Inc.