The sun protection factor (SPF) of sun screens is based on how well they appear to protect against sunburn (caused by ultraviolet B light (UVB). Unfortunately, this tells the buyer little about their ability to protect against skin cancer (caused by ultraviolet A light (UVA). Studies show that four to seven hours in the Mediterranean sun can cause irreversible damage to skin DNA, leading perhaps to skin cancer.

Ed.- Using sun screens are dangerous for two reasons. Firstly, by protecting against sunburn, they encourage people to expose their skin to the sun for longer periods, increasing their risk of skin cancer. Secondly, some of the chemicals they contain have now been linked with skin cancer.

Exposing the skin and eyes to sunlight is vital to good health (the manufacture of vitamin D3 by the body). See also Leave the sunscreen at home

In 2000, Linco Care was prosecuted when its Cabana Sun Protection Factor (SPF) 35 was found to only be factor 10. Its Looney Tunes sunblock was also found to offer only half the protection it claimed. In 2001 the Consumers' Association also exposed Sea & Ski Kids Colour Sunblock. Laboratory tests found that it was SPF 12 rather than the SPF 30 it claimed.

When a product claims to be sun factor 15, it is claiming that it permits you to stay in the sun fifteen times longer without burning. But actually this is only the case if you plaster on the same amount as was done for the tests. Researchers have discovered that most people apply about a third of that used for the test, reducing their protection proportionately.

Sun factor protection indicators are now to be applied to clothing. The minimum factor to be used - 30 - will be denoted by a blazing sun logo. The classification allows for wear, stretch and tear.