Sunlight can cause long-term damage to the skin's genetic heritage, DNA, which could result in skin cancer, says Dr Mark Birch-Machin of Newcastle University. Each year about 44,000 new cases of skin cancer are diagnosed in the UK and in the United States there are up to 1.2m new cases.
Many sun worshippers are only getting a fraction of the protection their sunscreen provides because they are applying it too thinly.
People who are overexposed to the sun suffer the short-term discomfort of burnt skin, but, says Dr Birch-Machin, they are rarely aware of the changes taking place in the DNA within their skin which can cause long term problems.
Dr Birch-Machin, a research lecturer in molecular dermatology, explains:
"Most people know that too much sun exposure causes sunburn - but few people realise that the Ultraviolet (UV) rays in sunlight cause DNA damage in the skin cells which may create a skin cancer time-bomb."
"Manufacturers rely on sunbathers applying the correct thickness of sunscreen to get the recommended protection from the UV rays. But people apply sun cream sparingly which is a false economy considering the risk of long-term damage to their skin DNA.
The protection offered by a sunscreen, defined by the SPF, (Sun Protection Factor) is assessed at an application thickness of 2mg/cm2. However several studies carried out by experts have shown that the general public apply much less than this amount - typically from about 0.5-1.3mg/cm2. Most users of sunscreens therefore only achieve 20-50% SPF of that expected from the product label.
Dr Birch-Machin says that UltraViolet radiation (UV rays) in sunlight can penetrate the skin layer and attack our DNA from childhood and cause permanent damage in the skin cells. UVA rays can form 'free radicals' which can alter the DNA, and UVB has a directly harmful effect on DNA.
"What is needed therefore is a reliable measure of how much UV exposure you’ve had over your life-time," says Dr Birch-Machin.
In this respect, his research team in Newcastle has shown a link between exposure to sunlight and damage to DNA that is found in mitochondria, which are the powerhouse of the cell. Compared to the DNA found in the nucleus of cells, the sun-damaged DNA in mitochondria is hardly repaired and so the damage piles up over time.
"It’s almost like a diary of sun-damaged DNA" he says.
But if sunbathers apply the correct thickness of sunscreen, they can prevent the UV rays reaching their DNA and avoid it being damaged.
Dr Birch Machin offers some advice on sun safety:
"Take care not to burn, avoid sunbathing during the hottest hours of the day (10am-4pm), cover up with loose-fitting clothes made from tightly woven fabric, wear a hat and sunglasses, wear high SPF sunscreen on exposed skin liberally applying it before going in the sun, re-apply sunscreen regularly particularly after bathing, take special care of babies and children"
Dr Birch-Machin predicts that one day doctors may be able to tell if you’ve spent too much time in the sun by measuring the amount of damage to mitochondrial DNA in skin cells.
This information from the ‘sun-damaged DNA diary’ could be important if it forewarns of skin cancer. In addition, Dr Birch-Machin’s research on sun-damaged mitochondrial DNA could be a useful tool to the cosmetic industry as it may be used to measure how well sunscreens work.
NB: For expert comment on this or any other issue relating to sun tanning/sun burn/skin cancer etc. contact Dr Mark Birch-Machin, Newcastle University, Tel: +44 (0)191 2085841 (home number +44 (0)191 2845575). E mail: M.A.Birch-Machin@newcastle.ac.uk.
Issued by Newcastle University press office, contact Claire Jordan tel 0191 208 6067/7850.
published on: 4th June 2001