A major innovation in Sun protection measurement The Integrated Sun Protection Factor-ISPF

摘要

Since the beginning of sun protection story,scientists and sunscreen manufac-tors have tried to find an universally and well recognised sun protection index,covering protection against all damaging sun spectrum wavelengths.Currently,SPF only reflects protection from UVB,the method being limited to the acute skin damage "sun burning".More and more,the scientific community and European regulatory authorities emphasize on the UVA part of the sun spectrum,responsible for acute and chronic skin damages and on the necessity to be protected during outdoors activities by broadband sunscreen products.However,there is no worldwide agreement on a method to measure the degree of UVA protection provided by a sunscreen preparation.The in vivo method based on persistent pigment darkening PPD has the disadvantage not only to measure a non real skin damage,but also to be limited to UVA irradiation,masking the syn-ergistic effects between UVB and UVA which probably complicate the real living skin response.We have discovered that the first impact of sun exposure toward the skin is the free radical production.The amount of free radicals increases according to sun exposure duration and decreases according to sunscreen protection.Thus,calculation of a global sun protection index is possible.We have called this new index Integrated SPF(I-SPF),because it quantifies a global protection level,covering the full range of the UV sun spectrum.Production of free radicals can be measured ex vivo and in vivo by using a special transformed ESR spectroscopy unit.A two step method is employed for the ISPF determination.In a first part,the relationship between UV dose and the amount of generated free radicals measured by ESR spectroscopy is established ex vivo unprotected human skin.In a second part,a sunscreen product is spread at the same amount as in vivo:2 mg/cm2.Accordingly,a protection factor could be calculated in the same way as the well-known in vivo SPF method:ratio of UV doses which are required to reach a same free radical production on protected and unprotected skin.Experiments show that ex vivo human skin can be replaced by pig ears skin.Different commercial sunscreen products were tested by the method.ISPF measured values ranged from 5 until 22,confirming our previous observations done on laboratory samples.Compared to the traditional SPF,the UVA filter efficacies are considered by the new protection factor:ISPF value dramatically drop down when the UVA filtration is not balanced to the UVB filtration.ISPF gives a better indication of the total protective effect of a sunscreen product as it includes any possible release of free radicals from the irradiated protective molecules.