Conventional wisdom is turned on its head yet again, this time on what kind of dress is best in a hot summer. No, it is not cotton or linen, but denim and wool, Swiss researchers say after reviewing 500 studies from around the world on how people protect their skin.

Writing in a study published online by the Lancet, they say using sunscreen is the least effective option.

The team from the Triemli Hospital, Zurich, Switzerland, said wearing clothes which cover the skin - plus hats and staying out of the sun - was the best method of protection.

But, as well as linen and cotton being less effective, light-coloured fabrics and those that are wet also offer low levels of protection.

Dr Stephen Lautenshlager, who led the research, said, 'Of course it can't be recommended to wear woollen fabrics on the beach. But it should be kept in mind that not every shirt blocks the UV radiation sufficiently.'

While covering up and staying out of the sun may well be the best option, it is 'deemed to be unacceptable in our global, outdoor society.'

'Sunscreens could become the predominant mode of sun protection for various societal reasons, for example healthiness of a tan, relaxation in the sun.' The team advises that when sunscreen is used the most important factor for its effectiveness is the application in a 'liberal quantity.'

But they warn that people tend not to apply sunscreen properly, only putting it on once they have already been exposed to the sun and applying too thin a layer.

And they add: 'Sunscreens should not be abused in an attempt to increase time in the sun to a maximum.'

Dr Kat Arney, Cancer Research UK's senior science information officer, said: 'This study confirms what we already know. Our Sun Smart Campaign has always said that sunscreen is the last line of defence in protecting skin against the sun's harmful rays.

'Many people do not use sunscreen properly and do not reapply it regularly and after swimming.

'Some believe sunscreen is an invisible shield that will give them carte blanche to lie out in the sun all day.'

Cancer Research UK advise staying in the shade when the sun is hottest - between 11am and 3pm - plus covering up with a T-shirt, hat, and sunglasses and using a factor 15 plus sunscreen.