Scientists have shown that manufacturers calculate Sunscreen Protection Factors(SPF) using a formula that assumes sunbathers apply four times as much lotion as they actually do.
SPF is a simple indicator for a buyer knowing how long they need to stay out in the sun, but as the study showed, most people apply a much thinner layer of lotion than they need to in order to benefit and be protected.
Therefore in practice, a sunscreen cream advertising an SPF of 16 actually offers a protection of two.
Professor Hans Christian Wulf of the University of Copenhagen, lead researcher said, " The factor on the bottles is more a level you may get if you did what they are doing in the test situation, but people are not doing that.
"Our results show that people who use sunscreen are less protected than they believe they are," Wulf said.
European manufacturers calculate the SPF by assuming 2mg of lotion is applied to every square centimetre of skin.
But according to the research team, a study they conducted on the Denmark beaches showed that the average amount applied by sunbathers was less than half- 0.5mg per cm squared.
In order to test the effect of a much lower application, the research team used Garnier Ambre Solaire SPF 4 to four patches of skin on the backs of 20 volunteers in doses of 0.5, 1, 2 and 4 mg per square cm.
After exposing them to a sun lamp and observing how long it would take for their skin to burn, they calculated the real SPF. They even used real UV filters to stimulate the effects of stronger lotions.
They found that an advertised SPF of 4 , 8 and 16, in reality offered a protection of 1.4, 1.7 and 2 respectively when sun bathers applied the average amount used.
The results were published in the British Journal of Dermatology.
A spokesperson for L'Oreal,which makes Garnier Ambre Solaire, said, " It is very difficult to draw a conclusion from this small study. However, we clearly state on our sunscreens that they should be applied generously and frequently.
So here's an eye opener to all tan loving sunbathers, apply four times the amount you do if you really want the SPF promised on your sunscreen. You might have to invest a lot more in sunscreen but it certainly beats sun burn and worse- cancer.