The study by consumer watchdog Which? found that the protection offered by Piz Buin 1 Day Long Lotion SPF30 (150ml), Riemann P20 Once a Day Sun Protection SPF30 (200ml), Soltan Once Invisible 8hr Sun Protection SPF30 (200ml), and UltraSun Family SPF30 (100ml) decreased by an average of 74 per cent between six and eight hours after application.
This means that SPF30 sunscreen could effectively be offering the protection levels of an SPF8 product by the end of a day in the sun.
Also part of the process were 11 regular SPF30 sunscreens, with even own-brand products from Asda, Lidl and Wilko all passing the test.
However, Hawaiian Tropic Satin Protection Ultra Radiance Lotion (180ml) was found to provide “significantly less” protection than it claimed.
Which? also noted that the “once-a-day” products are effectively banned in Australia as any claims that sunscreens do not need to be regularly reapplied are forbidden.
Director of policy and campaigns at Which?, Alex Neill, said: “Our testing shows that these sunscreens just don’t live up to their ‘once-a-day’ claims so people should reapply sunscreens regularly to ensure they have protection from the sun.
“With more than 100,000 people diagnosed with skin cancer in the UK each year, some manufacturers need to do more to ensure their sunscreens live up to the claims on the packaging,” she added.