Testing for cosmetics, the various strategies from the safety to the claim support: trends and good practices

TKS  Panel discussion – IFSCC issue (July-Aug)

Trends and strategies for in vitro and in vivo testing: from safety to claim substantiation

As a constant question for all actives ingredients or personal cares, talking about testing is a continuum in each step of the product development. Before other trends consideration, to choose the studies supports between all categories of test, the cosmeticians will have to define precisely the global context of its testing looking at the following points:

• The nature of the products : actives or finished products, lipophilic, suncare,
• The goal and duration of the assay: safety or efficacy,
• The studied claims: is it a mechanism of action such as oxidation, anti-pollution?
• The type of the results: screening, validation, benchmarking, publications or advertising,
• The regulation constraints linked to the country where the product is launched.

All this testing consideration refers to the regulation dedicated to safety or efficacy in each world zone and sometimes each country. In Europe, the reference is the European regulations for cosmetics and chemical ingredients with principally the OECD guidelines and the common Product Information File (P.I.F). In silico, in tubo, in vitro and ex vivo testing help progressively to have robust alternatives to animal testing. For the efficacy investigation in Europe, we must respect the 6 common criteria without specific norms (excepted sensory analysis and sun protection index cf. ISO) and to follow guidelines for Human testing (EEMCO, Good Clinical Practices…). These scientific objectivation processes protect the consumer from misleading claims and preserve the credibility of the cosmetic industry.

For preliminary testing (toxicology and safety), in silico, in tubo, in vitro and ex vivo are the more commonly used for both ingredients and finished products.

What is the challenge between in vitro/ex vivo and in vivo protocols for efficacy testing?

For in vitro assays there are notable distinctions between tests on human monolayer cells (primary or lines) used for hydrophilic substances for dilution reasons and tests on 3D reconstructed skin models, skin explants and 3D skin bioprint that can be used for lipophilic products. Monolayer cell tests have become a routine with a choice of a multitude of primary cells provided from various skin types and ages.

What really boosts the perspectives of in vitro tests ?

Obviously, the reliability and variety of the3D skin models. The studies using biopsies are almost rare.

Then, the manufacturers of reconstructed skins as well as the major testing laboratories are the real stakeholders of this constant innovation. To give the best predictive results, they offer sophisticated supports for the various claims and functions of the skin, hair, glands, cornea or mucosae…: integrating capillaries, melanocytes, neurons, sebocytes…

Coming in the market since almost 5 years, the number of bioprinted skin manufacturers rapidly increased offering a new way of innovation in France (CTI Biotech, Poieitis, SkinLab Creations…) and worldwide.

Beyond the assay duration that everybody would like longer, 3D skin models and ex vivo testing present undeniable benefits through:

• The multiple varieties of robust supports,
• The standardised assay conditions,
• The combination of assays with multiple action mechanisms,
• An ethical alternative to human testing when induced stresses are harmful,
• The quantitative and illustrative results.

But what about in vivo testing paradigm?

Cosmetics in life testing give through clinical studies a large amount of information about the tolerance, the functions and the performance of the cosmetics. The in vivo tests allow the multi-ethnic and tailor-made studies. Their protocols can combine an unbeatable multi-criteria approach including:

• Dermatologists and experts’ assessment,
• Insight of the subjects,
• Emotions analysis and sensory analysis,
• Instrumental measurements using high-tech devices,
• The imaging

In vivo testing can be seen as the pragmatic knowledge of the cosmetics performance on the consumers when linking with personalised diagnostics, home devices, marketing app. Naturally, it will follow the trends of the Internet of Thing (mirrors…), the AI using algorithms, modelling and data treatment. Could we imagine, one day, that the consumers could visualise directly the efficacy of the products on his skin using a simple app ? Could a DNA analysis coupled with in vitro assays, give a personalised result on the skin microbiota or skin ageing … ? The future is bright for both in vitro and in vivo!

Read more p38-49 : https://www.teknoscienze.com/Contents/Riviste/Sfogliatore/HPC4_2019/46/