Chemists at the University of California Riverside say that this problem can be further compounded if the sunscreen does not contain an adequate UVA filter, on top of a UVB filter.
The team, led by Kerry Hanson, worked around the principal that exposure to UV light can lead skin molecules to generate harmful compounds called reactive molecule species, or ROS - highly reactive molecules that can cause oxidative stress in skin cells.
ROS can react with the various cellular components of the skin, which in turn increases the risk of visible aging such as wrinkles.
Although UV filters in sunscreen are known to cut down the amount of UV rays absorbed by the skin, the researchers say that over time these filters can penetrate below the epidermis layer, leaving the skin more vulnerable to UV radiation.
The researchers say that three filters - octylmethoxycinnamate, benzophenone-3 and octocrylene - which are widely approved by international regulation authorities for use in sunscreens, can actually generate ROS in skin exposed to UV radiation, heightening the potential risk of UV damage.
This, the research team noted, only occurs when these UV filters had already penetrated the skin's epidermis and sunscreen has not been reapplied to prevent UV rays from reaching the penetrated UV filters.
"Sunscreens do an excellent job protecting against sunburn when used correctly," said Hanson. "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."
Hanson suggests that the best means of avoiding this situation is to ensure that individuals use more advanced UV-filters that stay on the skin's surface for longer to avoild UV-induced ROS.
Likewise, in a note aimed at sunscreen formulators, he also says that mixing the UV-filters with antioxidants can help to prevent an increase of UV-induced ROS in the skin as the antioxidants contribute to a reduction in ROS levels.
The research is particularly pertinent given that 95 percent of the visible signs of aging are associated with UV exposure and about 90 per cent of a total life-time of UV exposure is obtained before the person is 18 years old.
Given that only a few UV-filters are available that effectively block UVA wavelengths, the research suggests that high quality sunscreens that include UVA filters are most effective at preventing future signs of ageing when used liberally and often on children and young adults exposed to the sun.
The study results will appear in the forthcoming issue of Free Radical Biology & Medicine. In the meantime the research team says that the next project it will be working on will involve investigating the effect of smog on ROS generation in the skin.