For those of you who find the mess, smell and cost of slapping on the factor 20 a major seasonal irritation, there is good news, of a sort. 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 the middle of summer thinking that 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. And they don't apply enough, because it is messy, boring and expensive. For all these reasons, they get cancer."

Skin cancer is the most common form of cancer in the UK. Its most deadly form, malignant melanoma, affects more than 8,100 adults in Britain each year, killing almost 2,000 of them. "Fair-skinned or freckly people are most at risk," says Hawk. "Black and Asian skins tend not to get cancer, but they do age in the sun." Men are particularly bad at sun protection (studies show they tend to think putting on cream or lotions is unmasculine).

Anything that stops you getting sun on your skin is going to reduce your chances of melanoma (and could mean fewer wrinkles). But, says consultant dermatologist Dr Richard Turner, of the Churchill Hospital in Oxford, "We've got it round the wrong way. Sunscreen really should be the last resort. Your first priority should be to stay out of the sun. If you are in the sun, protective clothing will protect you better than sunscreen."

Of course, allowing for the fact that many people will strip off on a hot day, your final line of defence for the bits of your body that are not swathed in fabric should be to use an effective sunscreen and use it properly. But choosing which to wear can be an ordeal.

At one end of the scale lie exclusive cosmetic brands such as Doctor's Dermatologic Formula (DDF), offering high-performance sunblock in skin-flattering tints with other cosmetic bells and whistles. Then there are the appealing imports from companies such as Sunsense - Australia's leading brand now available in the UK (Australians are far ahead of the game when it comes to sun protection) - which offers a huge choice of gels, roll-ons, lotions and creams that come specially formulated for face, body, sport and even toddlers. There are also organic brands such as Green People, catering to those wary of chemicals, perfumes or colouring (although, says Hawk, there is no scientific evidence that the chemicals used in modern sunscreens are harmful to humans). And finally, there are the legions of household names - from trusty Ambre Solaire, to Asda's own brand.

So which works best? It is more a matter of taste than science, providing you get the basics right. Your sunscreen should offer protection against both UVB and UVA rays. UVB rays are the real nasties, around in Britain from early March to the end of September, and are the main cause of burning, cancer and ageing, says Hawk; UVA rays are around all day, year round, and have mostly an ageing effect.

Getting too hung up on what sun protection factor (SPF) actually means - for instance, how many minutes an SPF 15 will allow you versus an SPF 30 - is basically pointless. "Since the protection will disappear after a couple of hours whatever SPF you are using, just go for the highest SPF you can find - 50 or above, if possible," says Hawk. This way, if you don't put on enough you'll at least get a bit more protection than you would with a lower SPF. And as for whether gel, cream, roll on, spray or lotion works best: "Just try a few until you find one you like," he advises.

But what about chemical sunscreens, which use ingredients absorbed by your skin to protect against the sun's rays? Are they better than the physical sun blocks, that form a barrier between your skin and the sun - typically using titanium dioxide or zinc oxide? "Both offer good protection against UVA and UVB rays if used properly," says Hawk.

Cosmetic frills aside, then, expensive sunblocks will not necessarily protect your skin any better than the cheap ones. "There are special tests and regulations: companies can't just make their SPF up," says Hawk.

But if you are still confused, try Boots. It has a simple star system for all creams sold in its shops (the best protection has five stars). Choose a high SPF, four or five star, UVB/UVA sunscreen. Combine this with avoiding the sun between 11am and 3pm, and covering up with decent protective clothing when you can, and you will do your skin a huge favour this summer - and beyond.

Cover up and be careful

How to beat the sun

1 Cover up: wide-brimmed hats are preferable to baseball caps. If you can see through the fabric of your clothes when held up to the light, so can the sun. Special sun protection clothing such as that used by surfers is a great idea for beach wear.

2 Choose the highest SPF you can find, with UVA/UVB protection.

3 Double your dosage: studies show we use only half to one third of the amount of sunscreen needed to get the SPF on the label.

4 Be thorough: if you miss a bit, that patch could burn. Sunburn doubles your chance of melanoma.

5 Reapply every hour or two. Sunscreens rub off and are absorbed - even if it is a high-SPF work of nanoparticled genius that claims to need only one application, assume that it will wear off in two hours maximum.

6 Think ahead: slather up 15 to 30 minutes before heading out in the sun, and again just before you step outside.

7 Avoid sun between 11am and 3pm: no sunscreen can protect you completely.

8 In Britain, protect yourself from the beginning of March to the end of September and year round if you care about ageing from UVA rays.