Melanin: Aging of
Skin and Skin Cancerby Diana Clarke http://yourskinandsun.com
"Ultraviolet (UV) radiation is responsible for 90% of visible signs of aging on skin of whites," says Dr. Michael J. Martin, former Assistant Clinical Professor in Dept. of Epidemiology and Biostatistics at University of California, San Francisco.
Blacks' skin, however, ages much slower.
Why are most dark-skinned blacks protected from harmful UV rays? Because compared to whites, blacks possess more melanin, pigment that gives skin its color.
Melanin
Melanin offers protection against UV rays for blacks and other dark-skinned people. Conversely, fair-skinned people are much less protected and more susceptible to skin cancer. Furthermore, albinos' skin offers no protection.
Although blacks' skin produces more melanin than whites', all skin has same number of melanocytes, cells that manufacture melanin.
Melanocytes manufacture melanin from an amino acid, tyrosin, with help of an enzyme, tyrosinase. In bottom layer of epidermis above dermis, UV light stimulates production of melanin in form of insoluble melanosomes. These surround epidermal cells, which move up to surface of skin. The result is a tan.
Blacks' skin produce more melanin, even in absence of sunlight, and their type of melanin, eumelanin, is more effective at blocking solar rays. However, white skin produces melanin only in presence of sunlight and after UV rays have penetrated lower portion of epidermis and have caused skin damage.
"Melanin also functions as an excellent free radical scavenger. It affects delicately designed lipids that hold moisture in stratum corneum (the outermost layer of epidermis). If skin loses its moisture, it becomes rigid and cracks," says Sergio Nacht, PhD., Senior Vice-President of Enhanced Derm Technologies, Inc. in Redwood City.
UV Radiation and Skin
UV-A has longest wavelength, is not filtered by ozone and passes through glass. It reaches earth all year long and amount is comparatively stable. It can penetrate skin down to dermis, beneath four layers of epidermis. It is responsible for most of visible signs of aging, due to damage to collagen and elastic fibers of connective tissue of dermis.
UV-A radiation also plays a role in development of sunburns and skin cancer. Tanning salon lamps emit a large amount of UV-A rays to generate tans, so American Academy of Dermatology does not recommend their use.
