TESTING 61
the values in a table on the right-hand side. And so this has shown that the most irritating surfactant is C, which is SLS, followed by SLES followed by CAPB and then the mildest of all was in fact the novel surfactant. This was very encouraging, because this is actually what we expected to see in line with industry knowledge about these different surfactants. For the first human in vivo experiments, we used three different cohorts of volunteers to look for reproducibility using clinical scoring and colour measurements. The in vivo data is presented without error bars just for clarity, but we have indicated where there is a statistically significant difference with an asterisk. We used the same batches of materials that were applied in the in vitro studies and we diluted them down to 0.3% to apply on to the human volunteers (Fig 2). What we saw was exactly the same rank order of irritation as was seen in the in vitro model. So we had two variants of SLS, just as an internal control, and you can see those as the grey and the blue lines. They produce a linear increase in skin irritation each day the product was applied, and then the SLES is next, and then you find that the novel surfactant and the CAPB are significantly milder ingredients. So whether we measure erythema or we measure clinical grading, we get the same results as we saw in vitro, which is very encouraging for the model. We also looked at some blends of
different surfactants knowing that these surfactants are actually used together in a wide range of applications in the industry (Fig 3). And a very common combination to be used is SLES with CAPB, where formulators are aiming to get the formulation with the best texture while minimising the irritation potential. For this purpose, we placed the data for the surfactant blends into a rank
ET50 120 100
Rank order of irritancy using linear extrapolation and logic equation
80 60 40 20 0 1 10 Time (h) Figure 8: Face mask comparison. February 2020 PERSONAL CARE EUROPE 100 B ET50 12.86 > A 14.42 > C >48 9.00
8.50 8.00 7.50
A B C D E Control
7.00
6.50 2 3 Day 4 5
Rank order of irritancy
D C A B
E (E45 Cream) Control
Figure 7: Mild surfactant formulations.
order of irritation potential. It actually supported what we expected to see, and what we wanted to show was whether we got direct comparison between in vitro and in vivo. Our rank order in vitro was C, A, B,
determination of 3 face mask formulations
followed by D. These results were replicated in vivo (Fig 4). In vivo, we also wanted compare
different ways of assessing skin irritation to find an objective way of doing it. This is
Cumulative irritation scores
21 7 4 2 0 0
Percentage of viability relative to untreated control
chroma a*
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