Skin sensitivity to sunlight is controlled by the genetic ability of an
individual to produce melanin....
(http://cric.chemres.hu/POL/ASP_Home/asp_bro2.html)
The average white skin can only produce melanin for 15 minutes a day (New
South Whales Cancer Council, 1987).
Skin cancer is usually a disease of white-skinned people. If your skin is
naturally brown or black you have some built-in sun protection and risk of
skin cancer is lower. (http://www.rushmoor.gov.uk/85.htm)
The lighter your skin colour, the less melanin your skin can make... and
the easier it can be damaged by UV rays.
(http://www.mb.doe.ca/ENGLISH/AIR/HLWS/health1/skin2.html)
...it takes several days for the body to produce this extra melanin.
(http://www.rushmoor.gov.uk/85.htm)
In some senses, suntans are "protective," but contrary to most people's
belief, they do not prevent sun induced skin damage....
A suntan is your bodies protective response to a harmful environmental
stimulus. When you have a tan, you have exposed yourself to lots of harmful
sun rays. (http://healthed2.shs.vt.edu/sun.html)
There is no such thing as a healthy tan: a suntan, not to mention a
sunburn, is an indicator of skin damaged by the sun. A suntan results from
the pigmentation change of melanin, the body's reaction as it tries to
protect itself from further sun damage.
(http://www.pluggedin.org/info/info.html).
Staying in the shade will not prevent skin damage; the UVA and UVB rays
reflect off sand, snow, water, roads, and buildings and UV rays penetrate
clouds and "haze". (ibid.)
Even tanning slowly and carefully is dangerous. Darrell Rigel, M.D.,
clinical assistant professor of dermatology at New York University,
Manhattan, maintains, "There's no such thing as a safe tan. That's the
key point. You have to think about why you tan. The body senses that it
is being injured by UV radiation and, to protect itself, it produces
melanin." (http://freenet.uchsc.edu/2000/prevent/cancer/suntan/skin.html)
The upshot: I'd suggest that unless you have a clinical vitamin D
deficiency you get enough sun. I ran by a couple of ads for melanin-
based sunblock as I looked for these references. It occurs to me that
using early genetic engineering it may be that increasing melanin in
the skin is easier than repairing/replacing damaged cells constantly.
During the time between then and full-scale nanotech/uploading, dark
skin may become quite fashionable as a longevity treatment. I think
that at that point a fair measure of a person's IQ (irony quotient)
could be how loud and long they laugh at that prospect.
Kennita
Kennita Watson | The bond that links your true family is not one of blood,
kwatson@netcom.com| but of respect and joy in each other's life. Rarely do
| members of the same family grow up under the same roof.
| -- Richard Bach, _Illusions_