ShareThisBy LEE BOWMAN
Here's another good reason to keep slathering on the sunscreen: If you don't, some of its filtering ingredients can break down into compounds that actually cause more damage to the skin, according to a new study.
Scientists at the University of California-Riverside, found that three ingredients widely used in sunscreens to filter ultraviolet radiation generate harmful compounds called reactive oxygen species when exposed to UV radiation in lower layers of skin.
Those reactive molecules can cause oxidative damage to cell walls, lipid membranes and genetic material inside skin cells, leading to skin damage and increasing the visible signs of aging.
Exposing unprotected skin to sunlight also generates the reactive molecules, the researchers note, but in fewer numbers than when the sunscreen chemicals are present below the outermost layer of skin.
However, the researchers note that the additional reactive molecules are generated only when the UV filters have penetrated deeply and when sunscreen has not been reapplied to prevent UV radiation from reaching the absorbed filtering chemicals.
"Sunscreens do an excellent job protecting against sunburn when used correctly," said Kerry Hanson, a senior research scientist in the chemistry department at UC-Riverside and lead author of the research, which was released online Monday by the journal Free Radical Biology and Medicine.
"This means using a sunscreen with a high sun protection factor and applying it uniformly on the skin. Our data show, however, that if coverage at the skin surface is low, the UV filters in sunscreens that have penetrated the epidermis can potentially do more harm than good."
For the study, Hanson and colleagues applied sunscreen to the surface of skin tissue samples to test the effect of sunscreen penetration on the reactive molecules below the surface.
They used a microscope with a fluorescent probe molecule that allowed them to see what was occurring beneath the skin surface. By comparing images taken before and after the skin was exposed to UV radiation, they could measure how much the damaging molecules increased after sunscreen penetration.
About 95 percent of the visible signs of aging to the skin are associated with UV exposure, and only a few filters are available that block UV-A, the wavelength of solar radiation that penetrates more deeply into the skin.
Hanson said that, ideally, more advanced sunscreens need to be developed that ensure UV filters stay on the skin's surface and reduce the chemicals' contribution to the damaging molecules. "Another solution may be to mix the UV filters with antioxidants, since antioxidants have been shown to reduce UV-induced (reactive molecule) levels in the skin," the researcher added.
Christopher Bardeen, an assistant professor of chemistry at UC-Riverside, in whose lab the studies were done, said for now "the best advice is to use sunscreens and reapply them often: the Skin Cancer Foundation recommends every two hours, especially after sweating or swimming, which can wash away sunscreen. This reduced the amount of UV radiation getting through to filters that have penetrated the skin."
On the Net: www.skincancer.org
www.sfrbm.org
