Two sun creams from leading brands are failing to provide the protection they claim, according to tests by a consumer watchdog.
Boots Soltan Protect & Moisturise Lotion SPF30 (200ml) and Hawaiian Tropic Silk Hydration Lotion SPF30 (180ml) both offered only around two-thirds of their claimed SPF (sun protection factor), Which? said.
The consumer group said the Silk Hydration Lotion was "worryingly" the second Hawaiian Tropic product to fail its tests in the last two years.
It has branded the creams as "don't buys" in its investigation, which used British Standard tests to check 13 products with an SPF of 30 on their SPF and UVA protection.
Piz Buin Ultra Light Dry Touch Sun Fluid SPF30 (150ml) and Hawaiian Tropic Satin Protection Sun Lotion SPF30 (200ml) both failed the tests last year, and Which? said it continued to recommend consumers avoid these products.
Sun creams are designed to protect skin from UVA and UVB radiation which may increase the risk of developing skin cancer. SPF indicates the amount of protection sunscreens offer against UVB, which is the main cause of sunburn.
Which? said effective products did not have to be expensive, finding "affordable" own-brand lotions from Asda, Morrisons, Tesco and Sainsbury's all offered the SPF claimed.
Which? executive director Richard Lloyd said: "We're very concerned that a further two popular sunscreens have now failed our tests."