Last week we hosted our very first webinar where our unique XtraMild™ mildness test took centre stage. Dr Carol Treasure and Chris Longmore looked at why mildness testing is so important, and how this super-sensitive method can be used to test a wide variety of products, including surfactants, wash-off formulations, leave-on products, and baby care ranges. Didn’t make it to the webinar? Here’s the 411…

The Recap

The importance of mildness testing

Dr Carol Treasure opened the webinar by focusing on why there’s a need for new tests to predict mildness. Carol delved into any contributing factors to the increased incidences of skin reactions, and stress came out on top with the World Health Organisation (WHO) describing it as the “health epidemic of the 21st century”. This is because stress puts our inflammatory reactions on alert and lowers the threshold to elicit a reaction. Other factors include air pollution, chemical exposure, frequent washing, hormonal changes, and poor diet, to name a few.

Around 37%* of consumers actively avoid certain skincare products as they are worried about a skin reaction. This highlights the demand from consumers for ever milder products, that they feel confident using even when their skin feels extra sensitive.

* Naldi et al (2014). Prevalence of self-reported skin complaints and avoidance of common daily life consumer products in selected European regions. JAMA Dermatol 150(2): 154-162

XtraMild: in vitro test for mildness – The method and data development

Chris Longmore, our scientific account manager, is up next and poised to answer the question: How do we intend to start predicting mildness for certain products?

It’s been well established that tissue viability has historically been used as a model of skin irritation. We use 3D human skin models, grown commercially in a lab, taken from human cells. These are an excellent model of human tissue with all the representative layers you’d expect to see in human tissue. The test items (a chemical ingredient or a finished formulation) can then be applied directly to the tissue surface – this gives us a good model of “real life” exposure. There are no solubility limitations for this test – we can apply a test item or formulation as we might do in real life.

In this test we take the tissue models and apply the test item for various time points (1, 5, 18, 24 and 48 hours). Some traditional tests for irritation only look at the result at a single time point whereas we want to see the effect a substance has over time. This will help us really tease out the differences between really mild items and the difference in viability that we see. The percentage of viability at each time point will determine the ET50 value which we can then use to place the test item into a category of irritation. We can also compare those values to find out not only the category but how two products compare, and which comes out milder.

Oh baby baby

Carol returns to focus on why mildness is particularly important when it comes to baby care. From safety drivers like maintaining pH balance of the skin, avoiding irritation to the skin and eyes, and ensuring microbiome integrity, to commercial drivers such as comparative information between multiple candidate formulations, mildness is key when it comes to developing baby care products.

Mildness testing in other tissues

Ocular irritection eyeEye mildness test

For our mildness to eye test, we use a human reconstructed cornea. This model has a really good simulation of the human cornea. The key difference between the eye and skin models is the eye doesn’t have the barrier the same as the skin – this makes it more vulnerable to irritating products. We use an ET50 type method, like XtraMild to skin. This test can be particularly important to package together with the skin test for any products that are going to come close to the eye: mascara, shower gel, shampoo etc.

The Q&A

What is the ability to test things other than surfactants using the XtraMild method?

Carol: Great question – we tend to focus on surfactants as they’re so commonly used. We can test pretty much every type of ingredient category using the skin models. Because we are dosing straight onto the surface of the skin models, we can control any concentration, any pH adjustments that we need to make. We are not dependant on the ingredients dissolving in the cell culture medium – which has sometimes been a limitation of some of the more basic cell culture techniques in the past.

In terms of methodology, are there any challenges in testing volatile products or products containing high amounts of alcohol?

Chris: This would need to be taken on a case-by-case basis. The test items are incubated on the tissue models at 36 degrees, if the test item is volatile and has a boiling point below that then it would boil straight off the tissue model. Depending on the test sample there could be some challenges associated. In that case we’d enter a conversation and think about what extra control we could build into the test.

How do your results compare to other mildness testing methods?

Carol: We’ve never done any direct comparison. Those methods have been around for a really long time and are fairly crude indicators of mildness. The advantage of what we’re doing is that we’re actually using tissue engineered skin, a real-life skin sample with simulated human physiology. Based on the feedback I’m getting, there is nowhere near the level of sensitivity or being able to differentiate between ultra-mild samples. They might not give as much of a detailed result.

Does this go beyond personal care? Can this be used for the different surfactants used in disinfectants for example?

Carol: This is something we’ve been doing for a long time. We have been running the skin ET50 methods for household products and other types of chemically based products. Sometimes this isn’t necessary to go up to 48 hours for these products but that’s why we work with companies to create more of a bespoke method to create the most appropriate course of action.

Does the 3D model address skin lipid considerations?

Carol: Yes. The skin barrier on EpiDerm™, work has been done on the lipid profile on that. Our friends at Mattek have done a lot of work in that area. The barrier is slightly thinner in vitro than it is in vivo. From a safety perspective this is erring on the right side because this means the models are actually more sensitive – if anything we are going to over-predict that irritancy potential.

We want to say a big thank you to everyone who signed up to our very first own-hosted webinar – look out for more to come in the future! Watch the webinar now.

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