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One of the most important facts you should know is that an epidemic of melanoma has broken out among indoor workers. These workers get 3 to 9 times LESS solar UV exposure than outdoor workers get, yet only indoor workers have increasing rates of melanoma.
There are two major factors that help explain this, and the first has to do with the type of UV exposure.
There are two primary types of UV rays from sunlight, the vitamin-D-producing UVB rays and the skin-damaging UVA light. Both UVA and UVB can cause tanning and burning, although UVB does so far more rapidly. UVA, however, penetrates your skin more deeply than UVB, and may be a much more important factor in photoaging, wrinkles and skin cancers.
A study in Medical Hypotheses suggested that indoor workers may have increased rates of melanoma because they’re exposed to sunlight through windows, and only UVA light, unlike UVB, can pass through window glass. At the same time, these indoor workers are missing out on exposure to the beneficial UVB rays, and have lower levels of vitamin D.