| "Ultraviolet (UV) radiation is responsible for 90% | | | | American Academy of Dermatology does not |
| of the visible signs of aging on the skin of whites," | | | | recommend their use.UV-B radiation, which is |
| says Dr. Michael J. Martin, former Assistant Clinical | | | | partially filtered by the ozone, penetrates the skin |
| Professor in the Dept. of Epidemiology and | | | | to the bottom layer of the epidermis where the |
| Biostatistics at University of California, San | | | | basal cells are produced. UV-B can break the |
| Francisco.Blacks' skin, however, ages much | | | | molecular bonds, disturbing the dividing cells and |
| slower.Why are most dark-skinned blacks | | | | altering their structure. Compared with UV-A, |
| protected from harmful UV rays? Because | | | | UV-B is responsible for most of DNAs damage. It |
| compared to whites, blacks possess more | | | | also causes most sunburns. During a sunburn the |
| melanin, the pigment that gives skin its | | | | reddening of the skin, erythema, is caused by |
| color.MelaninMelanin offers protection against UV | | | | dilation of capillaries.More UV-B is present during |
| rays for blacks and other dark-skinned people. | | | | summer months between 10 a.m. and 4 p.m. and |
| Conversely, fair-skinned people are much less | | | | at latitudes closer to the equator. Furthermore, at |
| protected and more susceptible to skin cancer. | | | | high altitudes the air is thinner and cleaner, so |
| Furthermore, albinos' skin offers no | | | | UV-B radiation is more abundant.UV-C, which is |
| protection.Although blacks' skin produces more | | | | generally filtered by the ozone, has the shortest |
| melanin than whites', all skin has the same number | | | | wavelength and the most energy, or intensity. It |
| of melanocytes, the cells that manufacture the | | | | can sterilize hospital equipment and kill bacteria.In |
| melanin.Melanocytes manufacture melanin from an | | | | addition, UV light that reaches the earth is |
| amino acid, tyrosin, with the help of an enzyme, | | | | scattered in all directions, and up to 85% is |
| tyrosinase. In the bottom layer of the epidermis | | | | reflected from surfaces.The Theory of Melanin |
| above the dermis, UV light stimulates the | | | | for Environmental AdaptationOriginally, people of a |
| production of melanin in the form of insoluble | | | | particular race resided in a particular area. As time |
| melanosomes. These surround the epidermal cells, | | | | went on, their skin adapted to the environment. |
| which move up to the surface of the skin. The | | | | For instance, people who lived geographically close |
| result is a tan.Blacks' skin produce more melanin, | | | | to the equator had darker skin, and people who |
| even in the absence of sunlight, and their type of | | | | lived far from the equator had lighter skin.In |
| melanin, eumelanin, is more effective at blocking | | | | Scotland, which lies at a northern latitude, |
| solar rays. However, white skin produces melanin | | | | descendants of the Britons have white skin. When |
| only in the presence of sunlight and after the UV | | | | their skin is exposed to the meager sunlight, the |
| rays have penetrated the lower portion of the | | | | scant amount of melanin their skin produces is |
| epidermis and have caused skin damage."Melanin | | | | unable to block the sunlight. Therefore, their |
| also functions as an excellent free radical | | | | bodies are able to make Vitamin D with the help |
| scavenger. It affects the delicately designed lipids | | | | of sunlight. Vitamin D, a vitamin found in fish oil, is |
| that hold moisture in the stratum corneum (the | | | | necessary to prevent rickets, a bone disease |
| outermost layer of the epidermis). If the skin | | | | caused by too little calcium.In contrast, in Africa, |
| loses its moisture, it becomes rigid and cracks," | | | | which is near the equator, blacks require intense |
| says Sergio Nacht, PhD., Senior Vice-President of | | | | sunlight to penetrate their dark skin to make |
| Enhanced Derm Technologies, Inc. in Redwood | | | | Vitamin D. This is all well and good. However, |
| City.UV Radiation and SkinUV-A has the longest | | | | when blacks lived in England during the Industrial |
| wavelength, is not filtered by the ozone and | | | | Revolution, they were the first to develop |
| passes through glass. It reaches the earth all year | | | | symptoms of rickets, such as retarded growth, |
| long and the amount is comparatively stable. It | | | | bowed legs and fractures because not enough |
| can penetrate the skin down to the dermis, | | | | sunlight was available.Fortunately, in 1930, Vitamin |
| beneath the four layers of epidermis. It is | | | | D was discovered and dispensed as a supplement |
| responsible for most of the visible signs of aging, | | | | to add to the diet.On the other hand, the skin of |
| due to damage to collagen and elastic fibers of | | | | whites in Australia are in complete opposition to |
| the connective tissue of the dermis.UV-A radiation | | | | their climate. Consequently, intense UV radiation |
| also plays a role in the development of sunburns | | | | has been the major cause of skin damage and |
| and skin cancer. Tanning salon lamps emit a large | | | | skin cancer Down Under. |
| amount of UV-A rays to generate tans, so the | | | | |