$Unique_ID{BRK01295}
$Pretitle{Skin and Subcutaneous Tissue}
$Title{What Causes a Tan?}
$Subject{sun tan dangers cancer}
$Volume{L-20}
$Log{}

Copyright (c) 1991   Tribune Media Services, Inc.


What Causes a Tan?


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QUESTION:  While everyone now is warning against the dangers of a sun tan, I
still don't understand what causes a tan?  If the body produces this naturally
isn't it a good thing?  While your at it perhaps you can explain just what
causes a sun burn as well?  I know that isn't too good for you.

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ANSWER:  Obviously a sun burn with its painful consequences is something to
avoid, and can rapidly change a fun weekend into something far less enjoyable.
Actually there are four effects upon the skin from exposure to the ultraviolet
(UV) radiation in the sun rays, all of which attempt to reduce the injurious
effects of the sun's rays.  They are erythema, short-term tan, common tan, and
delayed thickening of the skin.  Erythema is the name given to the red flush
that occurs to the skin after exposure. to sun rays (as well as a variety of
other causes).  A substance called prostaglandin is released by the tissues
which causes the capillaries in the skin to dilate (open), fill with more
blood and give the red coloring to the skin.  This is an attempt to protect
the skin and reduce the damage from the sun's rays.  It comes on from 2 to 12
hours after exposure and its severity is related to the amount of exposure.  A
short-term tan is caused by ultraviolet A rays, is created by the oxidation of
the melanin (pigment) in the skin and fades away in a day or two.  The common
tan takes several days to develop, and is caused by the production of more
pigment in the skin as a response to the sun's ultraviolet B (UVB) rays,
pigment that acts as a protection for the skin the next time it is exposed to
the sun.  Over a period of time, perhaps several months, the upper layers
(epidermis) of the skin thicken.  These thick skin layers can also absorb the
UVB rays, and reduce the amount of harmful radiation that reaches the lower
(basal) layer of the skin.  A word about protection.  Of the 1 million new
cancers that are diagnosed each year, about 30 percent occur in the skin, and
are thought to be provoked by chronic exposure to UV radiation.  A person with
a history or more than six serious sunburns in a lifetime, is 2.4 times more
likely to develop a melanoma, a cancer that spreads rapidly through the body
and which can be lethal.  If exposure to the sun can't be controlled, be sure
to apply sunscreens with a sun protection factor (SPF) of at least 15 to cut
down your exposure to these potentially harmful rays.
ÿ
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The material contained here is "FOR INFORMATION ONLY" and should not replace 
the counsel and advice of your personal physician.  Promptly consulting your 
doctor is the best path to a quick and successful resolution of any medical 
problem.
