Think twice before applying a sunscreen lotion, for if used inappropriately, it may end up damaging your skin, researchers at the University of California have found.

Filters in sunscreens that keep out ultraviolet radiation can generate compounds that attack skin cells, researchers asserted.

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.

The researchers said that when sunscreen is applied on the skin, special molecules called UV filters contained in the sunscreen, cut down the amount of UV radiation that can penetrate the skin. Over time, though, these filters penetrate into the skin below the surface of the epidermis, the outermost layer of skin, leaving the body vulnerable to UV radiation.

"Sunscreens do an excellent job protecting against sunburn when used correctly. This means using a sunscreen with a high sun protection factor and applying it uniformly on the skin”, Hanson, who works in the laboratory of Christopher Bardeen, an assistant professor of chemistry at UCR, said.

“Our data show, however, that if coverage at the skin surface is low, the UV filters in sunscreens that have penetrated into the epidermis can potentially do more harm than good”.

“More advanced sunscreens that ensure that the UV-filters stay on the skin surface are needed; such filters would reduce the level of UV-induced ROS. Another solution may be to mix the UV-filters with antioxidants since antioxidants have been shown to reduce UV-induced ROS levels in the skin", he added.

The researchers concluded by saying that the best advice is to use sunscreens and re-apply them often – the Skin Cancer Foundation recommends every two hours.

One should also reapply sunscreen creams after sweating or swimming, which can wash away sunscreen so that it reduces the amount of UV radiation from getting through to filters that have penetrated the skin.