Fatigue Symposium 2025: New Insights Into Hair Breakage

Hair fatigue testing has rapidly grown, from a niche topic, into a mainstream technique for hair claims testing. With this fast rise in popularity has come a demand for better, consumer validated protocols, and a need to understand, more fully, what the data are telling us about hair breakage. It is for this reason that TRI organised the ‘Symposium on the Fatigue Testing of Hair’ on Thursday 15th May. This event, co-organized with Dia-Stron Ltd (UK), was a hybrid event, and attracted 103 hair fatigue testing enthusiasts, roughly 20 of whom attended in person at TRI.

Dr Trefor Evans presenting at the Symposium

The event started with a presentation from Dr Trefor Evans (TRI Princeton) titled “An Introduction to Single Fiber Fatigue Testing”. Trefor, one of the pioneers of hair fatigue testing, showed how breakage in fatigue tests was a different thing to breakage in traditional tensile testing, and how fatigue failure was often more sensitive to hair treatments. Next came a presentation from Dr Rebecca Lunn (Dia-Stron Ltd) titled “Cyclic Fatigue Measurements in the Cosmetics Industry”. Her presentation informed us of the different types of fatigue protocols that can be used, and the pros and cons of each. Rebecca’s message was that we should always consider the instrument settings used when looking at and interpreting fatigue data. Very different conclusions can be drawn from different protocols applied to the same set of samples!

The third presentation was given by Prof Anthony Bunsell, titled “The Science of Fatigue of Fine Fibres”. Anthony brought us insights from the wider materials science world and showed us how cracks formed and propagated in synthetic fibres. His talk reminded us of the importance of using imaging techniques to understand fracture formation and breakage mechanisms. The final talk of the morning was given by Dr Lynsey McColl (Select Statistical Services) and was titled “An Introduction to Survival Analysis”. In the talk, Lynsey, explained how survival analysis works, and can be applied to fatigue testing for testing the significance of treatment effects. She described the log rank test, and an interesting alternative, the Cox Proportional-Hazard model.

The afternoon of the Symposium was given over to the applications of fatigue testing in hair science and claims testing. The first talk in the afternoon was given by Dr Jennifer Marsh (Procter & Gamble), titled “New Insights from Fatigue Measurements of Consumer Hair & Correlation with other Damage Measures”. This presentation showed how it is possible to validate a fatigue protocol versus consumer perception using hair samples taken from volunteers. Jennifer also showed how their experiments suggest that both protein and lipid changes probably drive hair breakage. The next talk was given by Jessica Welzel (Henkel) titled “Fatigue Failure Behaviour of hair From Different Geographical Origins in Strain-Controlled Experiments”. As the title suggests, this work showed how fatigue failure behaviour depended on geographical origins of the volunteers, and how differences in fibre structures were probably driving these differences.

Next in the afternoon, was a presentation from Dr Nawel Bahdadhi (L'Oréal) titled “From Science to Disruptive hair Repair Consumer Perceived Innovation Technologies”. This presentation showed how fatigue testing was being used by L'Oréal to support hair strength claims for the Kérastase Premiere range, and how the fatigue results were supported by a range of other techniques, including DSC testing and consumer testing.

To wrap-up, Dr Trefor Evans (TRI), proposed some technical questions to the audience in a presentation titled “Where do we go from Here?”.

Discussions then ensued about:

• Why do some consumers have very breakage resistant hair?

• Given the different methods used across the industry, what protocols are best practice, and how should we validate them against consumer perception?

• How should fatigue data be properly interpreted?

Feedback from attendees on the Symposium has been universally positive. Clearly, putting time aside to discuss and debate one technique in great depth was a very useful exercise, and is something that TRI will look to doing again in the future.

All the content from the Symposium will be put onto the TRI Library in 2-3 months’ time. People who registered can access the slides and video content for the next 3 months at https://cvent.me/5YmdLR

Previous Symposia and Conferences can be found in the TRI Library as Box Sets https://library.triprinceton.org/all_box_sets/