Saturday, November 15, 2014

A 22-year-old woman comes to your office

A 22-year-old woman comes to your office concerned about sun exposure. She brings a few sunblock
creams into your office and wants to know which one is best for preventing wrinkling and blotchiness.

She is less concerned about sunburn because she is trying to get a better tan. Blocking which ultraviolet rays will achieve her desired result?

C. Both UV-A and UV-B equally
D. Neither UV-A nor UV-B

The answer is A.  The UV spectrum reaching the earth is arbitrarily divided into two major segments: UV-A and UV-B. The outermost epidermal layer, the stratum corneum, is a major absorber of UV-B, and less than 10% of incident UV-B wavelengths penetrate through the epidermis to the dermis. In contrast, UV-A readily penetrates t the dermis. Photons in the UV-B are 1000-fold more efficient than photons in the UV-A in evoking the sunburn response. UV-B is primarily responsible for the sunburn respons and for vitamin D photochemistry. UV-A is important in the pathogenesis of photoaging in human skin.


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