3.7. In Vitro Sun Protection Factor (SPF) Method

The SPF values of cosmetic formulations were obtained from absorption spectra measurements using the in vitro sun protection factor assessment [51,52,64], which is defined by:

where E(λ) is the erythema action spectrum and S(λ) is the spectral irradiance of terrestrial sunlight under defined conditions by the International Organization for Standardization [65]. The T(λ) corresponds to the optical diffuse transmittance of cosmetic formulations as a function of wavelength (λ) and the wavelength integration limits refers to the combined UVB and UVA wavelength range. For the in vitro SPF assay, photoprotective films of cosmetic formulations were prepared by application of cosmetic creams on Transpore^® tape, which is a UV-transparent substrate [64]. The spread amount of cosmetic formulation on the Transpore^® substrate was 2.00 ± 0.1 mg cm⁻² using doctor blade technique [66]. Absorption spectra of photoprotective films were recorded on a Perkin Elmer spectrophotometer, model LAMBDA 465 UV–VIS–NIR. The in vitro SPF measurements were realized in quadruplicate and SPF results were expressed as mean ± standard deviation ± confidence interval (confidence level of the 95%).