with a maximum difference of transmittance absolute value of 10%
at 300 nm for 10 min of exposure. Therefore, also Vitro-Skin should not be used for photo-stability measurements. In Fig. 7 the curves of absorption for each substrate considered, calculated as A =1 R T where R and T are the total reflectance and transmittance as in Fig. 3, are reported. It is interesting to notice that both Vitro-Skin and Transpore absorb UV radiation mainly in the spectral region in which they are photo-unstable.
3.3. Total absorbance/transmittance measurements of sunscreen
Each substrate has been tested with the application of seven different sunscreen products. The total absorbances A(l) are reported in Fig. 8. The curves are calculated as the mean of several data acquired; the reproducibility of the values has been found within 10%. The absorbance values give the respective transmit-
Fig. 5. Full spectrum photo-stability of Transpore (3M).
Fig. 6. (a) Full spectrum photo-stability of hydrated Vitro-Skin and (b) full spectrum photo-stability of not hydrated Vitro-Skin.
D.