November 8, 2011

How Skin Tans

(Ivanhoe Newswire) -- We all know that skin tans in the sun. The process has known links to ultraviolet (and specifically UVB) exposure, which leads to tanning only after it damages the DNA of skin cells. Now, researchers have uncovered a much speedier path to pigmentation.

Researchers say the newly discovered response is likely to provide rapid protection against UV damage. Understanding how it works could impact how sunscreens are designed in the future.

"Our work shows that a dedicated UV receptor allows skin cells to immediately detect and respond to UV light," Elena Oancea of Brown University was quoted as saying.

"We found that human skin detects light using a mechanism similar to that used by the retina, on a timescale significantly faster than was previously known."

That response happens within a matter of seconds because of UVA light. UVA accounts for about 95 percent of the ultraviolet radiation at the Earth's surface. UVB makes up the other 5 percent. While scientists knew UVA causes oxidative damaget to cells that leads  to tanner skin in a matter of minutes, the question was how?

Oancea's team found that exposure of pigment-producing cells from human skin to UVA leads to the early synthesis of melanin pigment in a process involving calcium release. What's more, the skin's UVA response depends on rhodopsin, a light-sensitive ingredient also found in the retina of the eye.

"Our findings show that both the eye and skin–the only two organs constantly exposed to solar radiation–use similar molecular mechanisms to decode light," Oancea was quoted as saying.

The studies show that melanin production can be measured in human skin cells within an hour of UV exposure. That's key because not only does melanin make skin darker, it also protects the skin. It does this by absorbing ultraviolet radiation and converting it to heat.

"We hypothesize that the early melanin production triggered by rhodopsin activation provides a first line of defense against ultraviolet light-induced damage," Oancea was quoted as saying.  "If this is the case, then this pathway and its protective capacity should be taken into consideration in the design and use of broad-spectrum sunscreens."

SOURCE: Current Biology, November 2, 2011