Due to the effect described, the absorbance curves recovered by the measurement of the substrates with and without the sunscreen were very different among them both in shape and absolute value. For these reason, absorbance and reflectance measurement curves are not meaningful by itself for labelling. Unless they are used to calclate parameters that correlates to in vivo measurements or they are used only are ured only to make a relative comparison between different products. Generally, the trend among different SPF products was maintained,except in the case ofthe product labelled labellef SPF 20 when applied on Transpore and product labelled SPF 15 when applie on PMMA in there cases, the transmittance curves intersected those of products with higher or lower SPF values curver heve been measured different times and results have been always confirmed. In the case of Transpore, a chemical reaction between sunscreen and the substrate could be the cause of this result.
Some measurement have been performed also on Transpore self-standing. As already mentioned, the application of the cream on this substrate is hard to perfrom due to the fagility of the tape. Results show that, in comparison with Transpore on quartz, the shape of the curves was maintained, but the values of transmittance were 10 time higher.