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UV-B radiation, which is partially filtered by
ozone, penetrates skin to bottom layer of epidermis where basal cells are produced. UV-B can break molecular bonds, disturbing dividing cells and altering their structure. Compared with UV-A, UV-B is responsible for most of DNAs damage. It also causes most sunburns. During a sunburn reddening of skin, erythema, is caused by dilation of capillaries.
More UV-B is present during summer months between 10 a.m. and 4 p.m. and at latitudes closer to equator. Furthermore, at high altitudes air is thinner and cleaner, so UV-B radiation is more abundant.
UV-C, which is generally filtered by ozone, has shortest wavelength and most energy, or intensity. It can sterilize hospital equipment and kill bacteria.
In addition, UV light that reaches earth is scattered in all directions, and up to 85% is reflected from surfaces.
The Theory of Melanin for Environmental Adaptation
Originally, people of a particular race resided in a particular area. As time went on, their skin adapted to environment. For instance, people who lived geographically close to equator had darker skin, and people who lived far from equator had lighter skin.
In Scotland, which lies at a northern latitude, descendants of Britons have white skin. When their skin is exposed to meager sunlight, scant amount of melanin their skin produces is unable to block sunlight. Therefore, their bodies are able to make Vitamin D with help of sunlight. Vitamin D, a vitamin found in fish oil, is necessary to prevent rickets, a bone disease caused by too little calcium.
In contrast, in Africa, which is near equator, blacks require intense sunlight to penetrate their dark skin to make Vitamin D. This is all well and good. However, when blacks lived in England during Industrial Revolution, they were first to develop symptoms of rickets, such as retarded growth, bowed legs and fractures because not enough sunlight was available.
Fortunately, in 1930, Vitamin D was discovered and dispensed as a supplement to add to diet.
On other hand, skin of whites in Australia are in complete opposition to their climate. Consequently, intense UV radiation has been major cause of skin damage and skin cancer Down Under.
Diana Clarke is the editor of the Sun and Your Skin at http://yourskinandsun.com. She is a California credentialed teacher, freelance writer, and president of her own company, Clarke Communications and Technology. Her sun protection articles have appeared in publications, such as the San Jose Mercury News, Saratoga News and a high school health magazine, Listen Magazine.
