58 TESTING
formulation is irritating or not. It does not actually describe how irritating that item is. For more sophisticated approaches today, we need to know how irritating that item is, not just whether it is an irritant or not. In order to achieve a more detailed
profile of irritation, more sensitive approaches such as the ET50 method are used. This measures cell damage over a time course rather than just a single time point. As a result, we are able to classify items as severe, moderate, mild or minimal or non-irritant, and to calculate an ET50 value, which is the time taken to reduce the viability of the cells in the model to 50% compared with untreated controls. These values then allow us to place items into a rank order of irritation. But there were still some limitations with this methodology, because it went out to a time of 18 hours and we wanted to look at something even more sensitive. There are several ways that irritation is
measured in vivo, including the dermatologist assessing the skin in real-life conditions or large panels of home use of products. But we wanted to look at patch testing because it is a controllable model, we can apply standard doses for standard times and the assessments are well established and have been since the 1950s or 1960s.
Patch testing uses the principle of maximising the exposure of the product to the skin by occluding it for a period of multiple days, and it can be up to 14, 21 days. The idea is that it is a very sensitive way of identifying ingredients or products which might be even very weakly irritant, but when used regularly by large numbers of people in the population, could lead to significant numbers of people having reactions to products. And of course, that
ET50 120 100
Rank order of irritancy using linear extrapolation and logic equation
80 60 40 20 0 1 Time (h) Figure 3: Irritation potential of surfactant blends (SLES / CAPB). PERSONAL CARE EUROPE February 2020 10 100 ET50 1.82
C > A > 3.85
B 5.59
A= SLES/CAPB blend 1 B = SLES/CAPB blend 2 C = SLES/CAPB blend 3 D = SLES/CAPB blend 4
> D 9.01
14 13 12 11 10 9 8 7 6
2 3 Day Rank order of irritancy Stepanol WA (SLS)®
SLS 70% SLES 70%
Cocamidopropyl Betaine Water
Novel Biosurfactant Figure 2: Using surfactants to determine the correlation with in vivo.
has a potential impact on branding integrity and reputation. So it is a well-established, very sensitive method. Cutest clients tend to choose it where they are looking at critical applications, so baby care products, facial products, personal hygiene products,
determination of surfactant blends
where they want a good safety margin on the likelihood of irritation for their products. Of course, it is used to support claims including ‘dermatologically tested’, ‘suitable for sensitive skin’ or ‘eczema-prone skin’, because we can choose the panel of
Cumulative irritation scores
16 14 9 4 0 0
4 5
* *
SLES 70% *
Cocamidopropyl Betaine
Stepanol WA (SLS) Biosurfactant SLS 70% B Water
Percentage of viability relative to untreated control
Chroma a* value
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92
