According to a recent study published in the Lancet, there is no conclusive proof that sunscreens actually prevent skin cancer. The only safe approach to sun protection is to stay out of the sun as much as you can and, if you are out in it, cover up with sun-protective clothing and a hat.

But this is not as damning of the sunscreen industry as it might seem. According to dermatologist John Hawk, a skin-cancer specialist and spokesperson for the British Skin Foundation, the problem does not lie in the products themselves - which can be very effective - but the way in which we use them. "Very good research suggests that most people don't use sunscreen properly," he says. "They go out on a cloudy day in middle of summer thinking they don't need sunscreen. Or they slap some on, but miss spots. They don't realise that they have to apply sunscreen 15-20 minutes before going out, and then every hour or two after that. For these reasons, they get cancer."