62 TESTING
primarily done with skilled nurses assessing irritation. It was interesting that skin temperature also correlated well with the formulations; E being the SLS, the most irritating, and C being the least good of the CAPB/SLES blends. And we see increased skin temperature at the irritated area, which was an interesting observation for us (Fig 5).
Finished product assessments One of the first studies that we did was to use some finished formulations that contain various mild surfactants (Fig 6). These comprised a range of shampoos and, in this case, we tested three different mild formulations against a standard industry formulation, a standard leading shampoo. We were able to show significant
difference between the specifically mild formulations which were all fairly similar to each other, and the standard formulation, shown in purple, which showed a much greater degree of damage to those skin cells within the model at an early stage of exposure. This differentiated the effects from each other providing a rank order of irritation in vitro of D being most irritating and then fairly subtle differences between C, A and B. We were curious to see whether those more subtle differences would be supported by the in vivo patch test data, and we found exactly the same rank order D, C, A and B in vivo, so it is encouraging to see just what a good correlation we are getting, even with these very mild products (Fig 7).
What we saw with these particularly mild
formulations compared to just dilutions of surfactant was that the degree of irritation is much less, hence the more scattered lines that you see when you look at the in vivo chromameter data. But this is where the instrumental measurements fell down. They were unable really to put the products in the right rank order because the difference was not very great between the variants. However, the expert nurses saw quite big differences in terms of the irritation scores. So D, which was the standard product, was shown to be much more irritating than any of the other three formulations and CuTest put them in exactly the same order as XCellR8 did. So it shows that the expert assessment of the skin is a more refined way than in vivo instrumental objective measures for seeing irritation, which for us was a slightly surprising but also a very validating result for the expertise of our nurses.
Face masks We looked at a range of face masks with one of our collaborators (Fig 8). This is a strong application for skin mildness testing, particularly for products that are applied to the face and left on for a short time such as these face masks. So it was interesting to compare these three, to calculate ET50 values. And we were told after we had completed this study that this really gave more evidence to what the company had already suspected about these three different formulations based on some initial
studies that they had done in vivo, actually they had previously done a few in vivo studies and they had already demonstrated that C, which we have shown to be the mildest product here, was also shown to be milder and they had a few formulation concerns that were subsequently addressed about A and B. So our rank order of irritation was B followed by A followed by C, but C stood out as being quite different. This was the same rank order that Cutest saw for the three face masks (Fig 9). Again, because these are so subtly irritating, these are not highly irritating products as you would expect from a surfactant, the Chromameter again failed to show the sorts of differences as clearly as the clinical examinations did. So we could see that there were differences in the formulations which were in the same order as we saw in vitro. Again, this is very encouraging for their correlation.
Applications We have shown clearly that both methods provide valuable claim support data for skin mildness, which is one of the priorities for the market in cosmetics and personal care today. In addition, the in vitro screen could also be used as a valuable alternative or pre-cursor to clinical studies for either ethical or scientific purposes. For example, if there were suspicions about the irritation potential around a particular formulation, there are ethical reasons why it may be useful to screen that in vitro before going
9.00
A B C D E
Rank order of irritancy
B A C D (E45 Cream) E
Cumulative irritation scores
11 5 2 5.5 2 5 2 Figure 9: Face mask comparison. PERSONAL CARE EUROPE February 2020 0 3 5 8 Day 10 12 15 8.50 8.00 7.50 7.00 6.50 6 * *
chroma a*
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