Sunscreens May Damage the Skin

Are sunscreens always beneficial, or can they be detrimental to users? A research team led by UC Riverside chemists reports that unless people out in the sun apply sunscreen often, the sunscreen itself can become harmful to the skin.
When skin is exposed to sunlight, ultraviolet radiation (UV) is absorbed by skin molecules that then can generate harmful compounds, called reactive oxygen species or ROS, which are highly reactive molecules that can cause "oxidative damage." For example, ROS can react with cellular components like cell walls, lipid membranes, mitochondria and DNA, leading to skin damage and increasing the visible signs of aging.
In their research, Hanson and colleagues used epidermal model tissue and applied sunscreen to the surface to test the effect of sunscreen penetration on ROS levels in the deep epidermis. A two-photon fluorescence microscope allowed them to visualize ROS generation occurring below the skin surface. The ROS activity was detected using a probe molecule whose fluorescent properties change upon exposure to ROS. On comparing images taken before and after the skin was exposed to UV radiation, they found that ROS generation in the skin increased after sunscreen penetration.
"For now, the best advice is to use sunscreens and re-apply them often -- the Skin Cancer Foundation recommends every two hours, and especially after sweating or swimming, which can wash away sunscreen -- to reduce the amount of UV radiation from getting through to filters that have penetrated the skin," Bardeen said. "This, in turn, would reduce ROS generation."