Friday October 7 2011
Tanning devices can expose users to high levels of UVA
“Sunbeds may be even more dangerous than previously feared,” the Daily Mail has today reported. The newspaper said UVA rays, the main type of ultraviolet light emitted by tanning devices, has been found to cause the type of DNA damage that can lead to cancer.
The news is based on laboratory research that compared the DNA damage caused by UVA rays to that from UVB rays, which are already known to cause skin cancer. While UVB has long been linked to burning and skin cancer, UVA has previously been considered to be relatively harmless. However, this research builds on other studies that have suggested that UVA is not harmless and, like UVB, can lead to changes in the cell that increase the risk of skin cancer.
By exposing different areas of volunteers’ skin to UVA and UVB and examining skin tissue samples, the experimental study found that both could cause similar types of DNA damage, but that UVA tended to affect cells deeper in the skin. However, UVB affected cells at the surface of the skin more.
This research emphasises the need to use an appropriate-strength sunscreen that protects against both UVA and UVB. These sunscreens may be labelled as offering “broad spectrum” protection, and rated according to a five-star system in the UK. Cancer Research UK recommends that people use sunscreen of at least SPF 15 and with at least four stars to get good balanced protection across the UV spectrum.
Where did the story come from?
The study was carried out by researchers from King’s College London. It was funded by The National Institute for Health Research, the UK Medical Research Council, British Skin Foundation and the British Association for Dermatology.
It was published in the peer-reviewed, Journal of Investigative Dermatology.
The Daily Telegraph and the Daily Mail both appropriately advised that people should consider UVA protection as well as UVB when choosing a sunscreen.
What kind of research was this?
This laboratory-based research looked at how UVA rays affected skin cells. Light from the sun contains two types of ultraviolet (UV) rays, UVA and UVB. UVB has a shorter wavelength and has generally been thought of as the major carcinogen in sunlight. However, the researchers say that the action of UVA needs further consideration as there are more UVA than UVB rays in sunlight. UVA is also the predominant wavelength generated by sunbeds, and has now been classified as a carcinogen.
UVB is known to causes chemical changes to our DNA. In some cases the body’s natural DNA repair mechanisms can repair the damaged DNA, but in skin cancers these chemical changes have not been fixed and lead to harmful mutations in the DNA sequence. In skin cancers caused by UVB, there is a characteristic pattern of DNA damage that the researchers term a “UVB signature”.
UVA is also known to cause mutations, but this was previously thought to be by an indirect mechanism (i.e. causing chemical changes to other molecules in the cell that may have a knock-on effect on the DNA). However, recent experiments on cells in a lab have shown that UVA may also cause a “UVB signature” in the DNA sequence.
As recent evidence suggests that UVA may cause mutations in a similar way to UVB, this has raised doubts over the belief that UVA may be “safer” than UVB. Given this uncertainty, the researchers devised a series of experiments to see what effect comparable doses of UVA and UVB had on skin cells.
What did the research involve?
The researchers recruited 12 volunteers with healthy skin. The participants had fair, white skin that either always burns and never tans, or usually burns and tans with difficulty.
The participants were exposed to each wavelength of UV on 1 cm2 areas of previously-exposed skin on their buttocks.
Twenty-four hours later, the researchers used three participants to find the minimum doses of UVA and UVB needed to produce just-detectable redness of the skin. The participants were then given doses of UVA and UVB, which were multiples of this minimum dose (half the minimum dose, 1.5 times and 3 times). The degree of skin redness was assessed using a red skin scale.
The researchers took punch biopsies, which involved using a small tube-like device to extract a 4mm plug of skin from the exposed site. They used the biopsies to look at chemical changes to the DNA. To see how well the body could repair and reverse the DNA damage, they performed another set of biopsies on the exposure sites 3, 6, 24 and 48 hours after the UV exposure and examined the changes seen.
What were the basic results?
The researchers found that the skin became redder with increasing doses of either UVA or UVB. However, when they applied increasing multiples of the minimum dose required to cause redness, UVB caused more redness than UVA.
When the researchers looked for DNA chemical changes in skin cells immediately after exposure, they found that UVB led to more of these changes in the top layer of skin, whereas UVA led to more changes in the deeper layers of skin. They also found that as doses increased beyond the minimum dose, UVB caused more detectable chemical changes to the DNA than UVA. Although both UVA and UVB produced one particular type of DNA change, UVB caused additional chemical changes that were not found in UVA-treated cells.
The researchers then attempted to see how well the cells could repair the DNA damage caused by UV exposure. They found that the rate at which the body could repair the DNA damage was similar for damage caused by UVA and UVB. They said that by 48 hours the majority of DNA changes caused by UVA had disappeared but that there was still some DNA damage with UVB. The researchers said that this was because a higher proportion of DNA had been damaged with the UVB dose.
How did the researchers interpret the results?
The researchers say that they had demonstrated for the first time that UVA can cause DNA changes similar to some of those caused by UVB, although UVB also causes additional chemical changes not seen with UVA exposure. They said that deeper layers of skin are particularly vulnerable to UVA-induced damage and that this has implications for public health policies, particularly the need for developing measures that protect against UV light at a broader range of wavelengths.
This research has shown that UVA can produce some similar damage to the DNA when the skin becomes red as UVB. The research also showed that these changes may increase the risk of developing skin cancer if not repaired by the body. Previously, it was thought that UVB caused burning and was the major carcinogenic component of sunlight, while UVA was considered to be relatively harmless apart from ageing the skin.
In recent times studies, including this one, have suggested that UVA may directly cause the type of DNA damage that can lead to skin cancer. This study emphasises the importance of choosing a sunscreen that protects against both UVA and UVB (often labelled as offering ‘broad spectrum’ protection).
The charity Cancer Research UK has highlighted that there is no international measurement of UVA production, although in the UK there is a five-star system to measure UVA protection (the higher number of stars indicates a more balanced protection against UVA). Sunscreens will also contain a (sun protection factor) SPF rating. Cancer Research UK recommends that people use a sunscreen of SPF 15 or higher, with at least four stars to provide good protection against UVA and UVB. The charity also says consumers should not use sunscreen that has been open for over 12 to 18 months, but should instead buy fresh sunscreen offering appropriate protection.
Newspapers covering this research have also correctly highlighted that sunbeds may have a particularly high UVA output. The Daily Mail includes a quote that the strength of these rays can be 10 to 15 times higher than the midday sun. People using sunbeds and tanning booths should be aware that there is currently no regulation to govern the type or strength of UV rays that sunbeds give out. Even brief use may carry some risk, particularly for people who have fair features, freckles, lots of moles or damaged areas of skin. Read Are sunbeds safe? for more information.