Just when we had all learned never to go out in the sun without a sunscreen, along comes another scare story that says they may not keep us safe after all.

Researchers have found that, in spite of widespread use of sun protection creams, rates of skin cancer - thought to be triggered by sunburn - are still increasing. In fact, studies have shown that people who use a sunscreen the most are more likely to show early signs of the disease.

This sounds sinister - as if the creams themselves are causing the disease they are intended to prevent. But the accepted explanation seems to be, not that sunscreens don’t work, but that people who wear them stay in the sun far longer than is safe.

So the expert advice is not to stop using a sunscreen, but to use it more wisely. After all, no sunblock offers total protection. Not only does it wash off, but it becomes less effective over time and needs to be reapplied regularly. You should choose one with a minimum SPF - sun protection factor - of 15. SPF is, generally speaking, a multiple of the length of time you are safe to stay in the sun without burning. If you are fair skinned, that may only be 10 minutes, so an SPF 15 cream should protect you for 150 minutes.

SPF refers only to the produt’s resistance to burning, reddening UVB radiation. Your sunscreen should also block the more penetrating UVA rays, which doctors now believe are implicated in the deadliest form of skin cancer, malignant melanoma. Look for a cream that specifies high UVAprotection.

While the way we use sunscreens may be the main reason why skin cancer rates are not falling, there is also some concern as to whether the products themselves are safe. This is hardly surprising, given the cocktail ofchemical ingredients. Only one of them - PBSA - has been shown to cause harm: it damaged DNA in test-tube experiments. But some researchers are concerned that sunscreens, which work by absorbing light energy and converting it to chemical energy, may harm or change cells in ways that are not yet understood.

The overwhelming message, however, is to keep using the products, but not to rely solely on large doses of chemical filters to prevent burning. The experts, killjoys that they are, advise us to wear broad-brimmed hats and closely woven clothes, and to stay in the shade between 10am and 4pm. “Binge” sunbathing is more harmful than graduated exposure, so be careful during that fortnight in Benidorm. And when you do apply a sunscreen, be generous with it: two tablespoons per application are recommended.