in vitro testing. To this regard, Gers-Barlag et al.[6] demonstrated
significant differences in their protection factor results using
quartz plates or Transpore, especially when the applied product
was irradiated before or during the tests. They also demonstrated
that Transpore is inappropriate for such tests because of an
unspecified interaction between sunscreen filters and the substrateVitro-Skin has been seldom used for photo-stability sunscreen
tests [23]. When exposed to either vis/IR or full spectrum
irradiation, the hydrated samples of Vitro-Skin underwent a
tremendous damaging. In particular, its hydrating component
evaporated rapidly wrinkling the sample. Moreover, the transmitance curve of the sample changed rapidly during the exposure as
illustrated in Fig. 6a. The not-hydrated sample did not undergo a
visible damaging when exposed to vis/IR irradiation, but when
exposed to full spectrum radiation it resulted not photo-stable
(Fig. 6b), 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