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Skin Tanning And Thickening
By peace | January 22, 2008
What is Sunlight: In addition to UV, visible and infrared radiation(heat), sunlight is composed of a host of other solar rays, such as cosmic rays, gamma rays, x-rays and radiofrequency radiation, but these are present in too small quantities at the surface of the Earth, or are of too low energy, to affect our skin. When these rays penetrate the Earth’s atmosphere, they are modified in various ways. For example, visible light is scattered by atmospheric oxygen and nitrogen molecules in such a way that it makes the sky look blue; in addition, some of the overall radiation energy is absorbed and some reflected back into space by these molecules, as well as by atmospheric water vapour, dust particles and other constituents. The result is that only about two-thirds of the solar energy arriving at the surface of the atmosphere penetrates to ground level, and this is made up of about 5% UV, 40% visible and 55% infrared radiation.
UVB is far more effective than UVA at causing DNA damage, mostly in the epidermis, and it is therefore much more likely to set off the sunburn response. Fair-skinned individuals, especially those with freckles and red hair, burn particularly easily in the sun because of their relative genetic lack of melanin. In fact they sometimes may not tan at all, whereas darker-skinned people will do so with relative ease. How well a tan develops is thus built into you from birth and depends on what types of skin you have.
Skin Tanning
What we see as a suntan is the presence of brown UV radiation-absorbing melanin pigment in the epidermis. This is released into the epidermal keratinocytes by melanocyte cells of the epidermal basal layer within a few hours of damage to their DNA by sunlight. The pigment is partly transferred to the surrounding basal keratinocytes, clumping protectively above their important cell nuclei, and partly to the keratinocytes above, which then gradually move to the skin surface in the normal way and are eventually shed. This tanning process provides some two to four times greater protection against subsequent UV exposure. This lasts until the tan fades as the superficial skin cells are discarded.
Nevertheless, the fact is that a sunlight induced tan is always associated with UV radiation-induced DNA damage and is maintained only as long as such damage continues to occur. Therefore, there is no such thing as a completely safe tan other than a fake one or the one that you were born with. Thus, genetically black skin provides around 10-15 times better protection against the sun than white, and brown skin about five times as much.
Skin Thickening
Your skin also becomes thicker within days of sun exposure, and this is so-called hyperplasia may last for weeks to months. This reaction appears to be a response to DNA injury — injury to the basal layer keratinocytes by UV radiation. Thus, within a day or two, once DNA repair has taken place, these keratinocytes begin to divide and multiply much more rapidly than normal, resulting in a several-fold thickening of the epidermis, particularly of the protective stratum corneum, while the dermis also thickens a little. These extra layers can then provide 5-10 times extra protection against the future effects of the sun, especially for the vulnerable basal epidermal layer. This thickening is usually more effective than any accompanying tan, especially in fair-skinned people.
The combination of tanning and thickening together however may give up to around 10-40 times increased protection, much better than a tan alone, albeit always at the expense of some permanent skin damage.
Topics: Health, Man's health, Woman's Health |
January 25th, 2008 at 2:03 pm
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