Why you’ve probably been using sunscreen all wrong your whole life

What exactly does SPF mean, and how does it help you beat the heat? Kit Yates explains what factor you should really be using, why – and how often to reapply

Are you a 50, a 30, a 15 or a ‘chance it with a low protection oil’? (AP)

Are you a 50, a 30, a 15 or a “chance it in the name of a tan” oil lover? We all identify with at least one of these, but do you really know what SPF means – or how to use it?

Most of us don’t, actually. And as a mathematician with two redheads in their immediate family, I know better than most how vital it can be to protect yourself from the sun’s rays; particularly now, when the UK is experiencing some of the hottest weather this island has seen since records began.

The Met Office has issued a heat “health alert” for this weekend, with temperatures expected to reach at least 30C.