According to one study, too little spread of sunscreen could lead to less than half of the intended level of protection.
Scientists have studied the DNA damage that causes UV rays on the skin of subjects with different levels of light.
Their study showed that when applied with less than the recommended two milligrams per square inch of skin, sunscreen is not as effective.
However, many people spread the lotion much thinner than that, as little as 0.8 milligrams per
At this level, an SPF 50 sunscreen would provide only up to 40% of the expected protection.
Participant samples showed that repeated exposure to UV light caused "significant" damage to unprotected skin. Radiation was low.
The damage was less as the thickness of the sunscreen increased.
Senior researcher Professor Antony Young of King's College London said, "There is no doubt that su nscreen provides significant protection against the carcinogenic effects of the sun's ultraviolet radiation."
"What this research, however shows that the way sunscreen is applied plays an important role in determining its effectiveness.
"Most people do not use sunscreen as tested by the manufacturers, it is better for people to use a much higher SPF than they think necessary."
Nina Goad of the British Dermatologists Association said that people should use a SPF of 30
She added, "In theory, an SPF of 1
"It also shows Why we should not. For sun protection, we only use sunscreen, but we should also use clothing and shade.
"An additional consideration is that when using sunscreens, we tend to miss the area of the skin and apply it too thinly."
The results are reported in the Journalal Acta Dermato-Venereologica.