EDINBURGH, Scotland, Aug. 5 (UPI) — Some parts of the body are much more resistant to tanning than others, so a consistent all-over tan may be impossible, researchers in Scotland say.
Study leader Jonathan Rees of the University of Edinburgh says researchers analyzed the skin of 100 volunteers exposed to six doses of ultraviolet B on two areas of the body — the back and buttock.
In addition, the volunteers were given an injection to minimize the rush of blood that naturally occurs after the skin is exposed to sunlight in the first 24 hours. The redness is often confused with the start of a tan, but it is the skin’s signal that it has been damaged.
After seven days, the volunteers’ skin was analyzed to find what color remained after the redness faded.
The color — considered a suntan — comes from the skin’s production of melanin, a defense that blocks the skin from absorbing too much harmful UVB radiation.
The study, published in the journal Experimental Dermatology, found the buttock is much more resistant to sunshine and this may explain why it is so hard to get an even tan all over the body.
“One of the real puzzles about melanoma is why the numbers of tumors differ so much depending on body site,” the researchers said. “Our work shows that in one sense we are all made up of different units of skin, which respond differently to sunshine.”
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