Why is it that hair exposed to the sun gets lighter, but skin exposed to the sun gets darker?
Beats me! I was puzzled, too, so I asked an expert. Professor Walter Quevedo, a leading expert on the biology of the skin, explained it to me this way: In the case of sun-induced bleaching of eumelanic (dark) black hair, hydrogen peroxide and superoxides (free radicals) induced by the UV component of sunlight,act to disrupt the melanin “granules” eventually to a degree where the products of disruption are no longer black. That lightens the shade of hair color. Remind your studentthat the hair is dead tissue, so those melanin granules, once bleached, cannot be replaced. Unlike hair, the skin is alive, The melanocytes of the epidermis are stimulated to produce greater numbers of melanin “granules” (melanosomes that actually are much more complicated than granules). The melanosomes are transferred in increased numbers from the melanocytes to keratinocytes of the epidermis causing the darkening (tanning) of the skin. The persistent darkness of sunburned ski, results from an inflammatory re
