A survey of 2,000 UK adults found one in five was unaware that the SPF rating does not mean protection against all sun damage – only that from UVB rays.
Protection against UVA rays has its own separate rating system.
The protection provided by sun creams and lotions against UVB rays, which cause sunburn, is denoted by the SPF or factor on the bottle.
But there are also ultraviolet A rays (UVA) to consider too, which penetrate the skin more deeply, causing it to age – but only one in three checked the UVA star rating when buying sunscreen, the survey found.
The UVA star rating ranges from zero to five and indicates the percentage of UVA radiation absorbed by the sunscreen in comparison to UVB.
Prof Jayne Lawrence, chief scientist for the Royal Pharmaceutical Society, said: “Clearly many consumers do not realize the SPF rating applies only to the amount of protection offered against UVB rays, not UVA rays – both of which can damage the skin and cause skin cancer.
“People should not have to pick their way through complicated dual ratings information to understand how sunscreen works and the amount of protection it potentially provides.”