The way people typically apply sunscreen provides, at most, about 40 percent of the expected protection, say researchers at King’s College in London. The reason: Most people put on sunscreen in a thinner layer than recommended by the manufacturers, which is 2mg/cm2.
In a small study, the researchers measured DNA damage caused by sun exposure when sunscreen was applied too thinly. They divided 16 fair-skinned men and women into two groups of eight. One group was exposed once to ultraviolet (UV) radiation similar to that of sunlight on areas of their skin that had no sunscreen or had been treated with a high-SPF sunscreen of varying thicknesses. The other group was exposed to varying UV radiation on five consecutive days with the same sunscreen applications.
Skin biopsies indicated that repeated UV exposure caused considerable DNA damage in areas where no sunscreen was applied, even when the exposure was low, and that the damage was lessened somewhat when sunscreen was applied in a too-thin layer and considerably reduced when the recommended amount of sunscreen was applied, even with high-dose UV exposure. Five days of exposure to high-dose UV radiation with sunscreen at recommended levels revealed significantly less DNA damage than one day's low-dose UV exposure without sunscreen.
According to the researchers, using a sunscreen with an SPF of 30 or more can provide better protection than a lower SPF even if you don’t apply it properly.
Sourced from: ActaDV