Kings College in London found that UVA was able to cause progressively more damage the deeper it went, wheras damage caused by UV type B tended to decrease. It was previously thought that the most severe damage at deeper levels was caused by UV type C, which is mostly absorbed by the Earth's ozone layer.

However, this new finding suggests that more care needs to be taken when in the great outdoors, with most scientists estimating that UVA accounts for about three quarters of the Sun's total UV emissions, and is twenty times more common than UVB, according to the study.

"The damage seemed to increase as it went through the epidermis," the study's UK-based lead researcher Antony Young told the ABC's AM program. 

"We think that is due to a form of backscatter, in other words, the damage goes through and is somehow reflected back."

Radiation such as UVB has been previously known to cause molecular lesions known as thymine dimers (or TTs) in skin cells. However, the damage was usually limited to the upper layers of the skin.

These new findings, however, seem to suggest that these TTs can also be produced by UVA in the deeper basal layer of the skin, the place responsible for cell division and replication.

Mutation at this layer could potentially lead to the growth of carcinogenic tissue.

"Our data suggest that UVA1 may be more carcinogenic than has previously been thought," reads the study abstract.

UVA is also less dependent on the position of the sun in the sky, unlike UVB, which increases the level of exposure.

The research has been published online in the Journal of Investigative Dermatology.

[via ABC]