SPF is best way to rate sunscreen effectiveness

Even dermatologists are best able to compare the effectiveness of sunscreens when presented with SPF values, a recent study suggests.The doctors tended to underestimate the effectiveness of sunscreens when they were presented with information on how much radiation is absorbed by the sunscreen, say the authors.“Ultraviolet (UV) radiation exposure from the sun and artificial UV sources is the major cause of skin cancer and premature skin ageing,” lead author Stefan Herzog told Reuters Health in an e-mail.“The sun protection factor (SPF) is the best known sunscreen parameter. It conveys a sunscreen’s effectiveness in protecting against the UV radiation that causes sunburn,” said Herzog, a researcher at the Max-Planck Institute of Human Development in Berlin.Herzog said the UV radiation that causes sunburn is also known as is erythema (redness)-inducing radiation, or EIR.“The SPF is defined as the ratio of the EIR dose that induces the first visible redness on sunscreen-protected skin to the EIR dose that induces the same redness on unprotected skin,” Herzog said.Herzog said that when it comes to skin damage, what matters is how much of the radiation is transmitted through the sunscreen to your skin and not how much is absorbed by the sunscreen.Doubling SPF, for example from 30 to 60, cuts the amount of radiation transmitted to the skin by half, thus protection is doubled, the researchers write in JAMA Dermatology.Herzog and his colleagues wanted to know whether dermatology experts are able to adequately assess differences in sunscreen protection based on SPF, the percentage of EIR absorbed by the sunscreen or the percentage of EIR transmitted through the sunscreen to the skin.A total of 261 dermatology experts from Germany, the US, Switzerland and Australia participated in the web-based test. The doctors were asked to assess the increase in protection for 10 pairs of sunscreens with different SPFs.Each sunscreen pair had effectiveness information presented as SPF, the percentage of EIR absorbed by the sunscreen or the percentage of EIR transmitted to the skin.The doctors were asked which sunscreen in each pair would protect a person longer and how much more effective one was compared to the other. On average, the doctors underestimated the protection ability of all the sunscreens, especially when they were presented with percentage of EIR absorbed. The underestimates were smallest when information was presented in terms of SPF.