Skin cancer is linked to sun exposure

The finding suggests sunscreens must protect against both UVA and UVB rays to provide proper protection.

University of Sydney researchers found UVA rays - which age the skin, but do not burn - can cause DNA damage.

The study, in Proceedings of the National Academy of Sciences, contradicts the view that UVB rays alone pose a cancer risk.

This is an important paper which adds new data to the growing body of evidence pointing to a significant role for UVA. Dr Catherine Harwood

Experts had thought that UBA rays pose less of a problem, because, although they penetrate deeper than the shorter wavelength UVB rays that cause sunburn, they were thought to have less impact on DNA.

However, the Australian researchers who examined skin tumours found evidence that UVA rays had damaged cells in the deep basal keratinocyte cell layer.

The basal layer contains the mother cells that ensure continual regeneration of the skin through cell division

But the researchers believe that UVB damage may be enough to make skin cells migrating out from this region highly vulnerable to cancer.

Profound implications

The researchers, led by Dr Gary Halliday, wrote: "The predominance of UVA mutations in the basal cell layer reinforces the pivotal role UVA may play in the malignant transformation of human skin.

"The importance of protecting the population not just from UVB but also from UVA irradiation has profound implications on public health worldwide."

The scientists examined tissue samples from 16 patients being treated for two different types of skin cancer at the Royal Prince Alfred Hospital in Camperdown, Australia.

Both types of cancer showed greater signs of basal skin layer damage from UVA than UVB rays.

The vast majority of UVB mutations were in the outer layers of the skin.

They said the widespread use of UVB-blocking sunscreens in Australia may have led to increased exposure to UVA.

Dr Catherine Harwood, a dermatologist at Cancer Research UK, said: "This is an important paper which adds new data to the growing body of evidence pointing to a significant role for UVA in the development of skin cancer.

"Although experimentally very thorough it is still a relatively small study, and the findings now need to be confirmed in similar larger scale studies.

"As the authors point out, confirmation of such a role for UVA may have major implications for public health initiatives to prevent skin cancer, as it becomes increasingly clear that the protection from both UVA as well as UVB is essential."