Which? claims that its tests showed that out of a total of 12 sunscreen products all currently available on the European market, four failed to meet the claimed SPF15 on the lablelling.
The consumer association says that tests were carried out under independent laboratory conditions, using volunteers who were exposed to UVB rays to assess for affects. On the other, hand UVA tests involved the sun screens being applied to assess radiation absorption levels.
The association said that Malibu and Wilkinson 'failed badly', achieving SPF 6 and 6.3 respectively, affording them a 'don't buy' recommendation. Likewise, Boots Soltan SPF scored an SPF of 8.6, also earning a don't buy recommendation.
Asda Sun System, which the retailer says has been recently reformulated and exceeds the SPF 15 rating given on the label, achieved an SPF rating of 11.5 in the tests, but did not receive a don't buy recommendation .
In response to the publication of the tests results in the July edition of the watchdog's monthly magazine, the sunscreen manufacturers in question have rushed to defend themselves, with Boots taking a particularly strong stand.
"We completely disagree with Which's findings on Soltan factor 15 and are now considering legal action" said Mark Hobbs, head of Boots suncare product development.
"We've tested Soltan independently and in our own laboratories and we are confident that it's safe and does exactly what it says on the bottle."
He added that the beauty retailer is keen to work with Which? but said it had been refused the opportunity to talk to the testing centre 'to help identify any errors being made'.
However, a number of products also performed extremely well in the tests, receiving 'Best Buy' recommendations. Those included Garnier's Ambre Solaire Moisturising Protection Milk, Lancome Soleil Soft-Touch Moisturizing Sun Lotion, L'Oreal Solar Expertise Advanced Protection and PIZ Buin In Sun, which all slightly exceeded the SPF 15 rating on the labels.
Which? says that it wants manufacturers of sunscreen products, 'to take our test findings seriously and re-label, reformulate or withdraw these products'.
Given the risks associated with exposure to the sun, the findings of the tests are likely to be debated within the industry for some time to come. But either way, the results do highlight irregularities in testing methods, which, at best, are leading to confusion amongst consumers.
The Which? tests follow efforts by the European Commission to ban misleading information or claims by sunscreen manufacturers. The initiative was introduced in May and is likely to lead to the Commission issuing non-binding recommendations to the industry towards the end of this year.