ISO 24443:2021 pdf download – Cosmetics — Determination of sunscreen UVA photoprotection in vitro.
4? Principle The test is based on the assessment of UV-transmittance through a thin film of sunscreen sample spread on a roughened substrate, before and after exposure to a controlled dose of radiation from a defined UV exposure source. Because of several variables that cannot be controlled with typical thin film spectroscopic techniques, each set of sunscreen transmission data is mathematically adjusted so that the in vitro SPF data yield the same measured in vivo SPF value that was determined by in vivo testing. As in vivo method can raise ethical consideration, any alternative SPF method, published as an ISO method, may be used. Samples are exposed to a specific measured dose of UV radiation to account for the photostability characteristics of the test product. The resulting spectral absorbance data have been shown to be a useful representation of both the width and height of the UVA protection characteristics of the sunscreen product being tested. The mathematical modelling procedure has been empirically derived to correlate with human in vivo (persistent pigment darkening) test results. 5 Apparatus 5.1? Spectrophotometer? specifications The spectrophotometer wavelength range shall span the primary waveband of 290 nm to 400 nm. The wavelength increment step shall be 1 nm. A spectrophotometer that does not have a monochromator after the test sample should employ a fluorescence rejection filter. The spectrophotometer input optics should be designed for diffuse illumination and/or diffuse collection of the transmitted irradiance through the roughened polymethylmethacrylate (PMMA) substrate, with and without the sunscreen layer spread on its surface. The size of the diameter of the entrance port of the spectrophotometer probe shall be smaller than the size of the light spot to be measured at the sample level (in order to account for stray light). The lamp in the spectrophotometer that is used to measure the transmittance shall emit continuous radiation over the range of 290 nm to 400 nm, and the level of irradiance should be sufficiently low, so that the photostability of the product is not unduly challenged (a xenon lamp is a convenient solution). Therefore, the UV dose during one measurement cycle should not exceed 0,2 J/cm 2 .