“As soon as you step out into the sun, your skin knows that it is exposed to ultraviolet radiation,” said senior researcher Elena Oancea, an assistant professor of biology at Brown University.
“This is a very fast process, faster than anything that was known before,” Oancea was quoted as saying by LiveScience.
Tanning, or the darkening of skin when exposed to sun, is a protective response. Melanin, the dark pigment responsible for darkening skin, is believed to protect skin cells from damage caused by ultraviolet radiation in sunlight by absorbing the radiation.
Ultraviolet radiation comes in two flavors: UVA and UVB. UVB rays have shorter wavelengths, and make up only a small portion of ultraviolet radiation from the sun. Such rays lead to darkening of the skin days after exposure.
UVB rays are typically linked with DNA damage that can cause skin cancer, although research has also linked UVA to cancer. UVA rays, by contrast, have longer wavelengths and are less intense, but account for the majority of ultraviolet radiation and lead to skin darkening much more quickly.
In the new study, published in journal Current Biology, the researchers focused on how UVA rays lead to darkening.
They studied the skin cells, called melanocytes, that produce the protective pigment melanin, and found that the cells also contained rhodopsin, a pigment previously found only in the retina of the eye where it detects light.