Breakthrough on hyaluronic acid penetration inside hair fibres and keratin interaction for a smoothing effect explained
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Presented by: Cloé Boira
Introduction: Hyaluronic acid (HA) is a key active ingredient in skincare products but its benefits for the hair has been poorly described. Hair is a specialized derivative structure of the skin and it is ideally organized to protect human scalp. The external cuticle includes overlapping layers of scales and acts as a barrier to protect the inner structure, mainly made of keratin. To date, the interaction between HA and keratin has only been described in the stratum corneum and no evidence of an interaction inside the hair has been established. Indeed, exploring penetration of such molecules through the hair fibres presents some challenges and offers new hair benefits. Regarding the feasibility, different techniques including confocal fluorescence microscopy, have been used for examining the penetration of tagged molecules. Unfortunately, some issues such as hair auto fluorescence compromise the results. Besides, due to the hair fibres composition only low molecular weight molecules have been described, so far, to be able to penetrate the cortex. In this work, we developed efficient methodology to follow hair penetration in non-invasive way. We then designed an optimized HA solution dedicated to haircare application based on optimal hair penetration.
Methods: Hair locks were irradiated or not with UVA and UVB and then washed with different shampoos. Low molecular weight hyaluronic acid (LMW at 1%), high molecular weight HA (HMW at 1%), or an optimized blend between low and high molecular weight HA (HA-Blend at 1%) were used. A different approach based on confocal Raman spectroscopy has been proposed to track the penetration of active ingredients directly through the human hair fibres. Then, the α-helix/β-sheet ratio of keratin was evaluated by Raman analysis to predict the smoothing effect. At the ex vivo level, photographs were analysed to measure hair strands length before and after four or eight hours in extreme conditions of humidity.
Results: The Raman Z-profile analysis has shown that for the non-irradiated hair locks, there was significantly 5.9 times more HA-Blend than the placebo into the cortex. Besides, the penetration of this optimal HA-Blend was significantly higher compared to the two other actives. Regarding the irradiated hair locks, there was significantly 1.8 times more HA-Blend into the cortex in comparison to the placebo. The HA-Blend significantly penetrated more than the two other actives into the cortex. Whatever the irradiation of the hair locks, no significant difference was obtained for LMW and HMW in comparison to the placebo. Besides, the HA-Blend significantly decreased the α-helix/β-sheet ratio by -10% in comparison to the placebo. We also showed ex vivo that the HA-Blend at 3% significantly decreased the spontaneous frizzing by -11% in comparison to the placebo.
Discussion: For the very first time, we have established an innovative study to prove the penetration of hyaluronic acid inside the hair cortex in rinse-off condition. Irradiation with both UVA and UVB damaged the hair and open cuticle, but only penetration of the HA-Blend was significantly higher than the placebo. Interestingly, even in the non-irradiated condition, the HA-Blend was significantly able to penetrate through the cuticle until the cortex. We have also demonstrated that this optimized HA-Blend decreases α-helix conformation and promotes β-sheet keratin conformation in order to smooth the hair. Thus, we have established that the direct interaction between HA and keratin is responsible for the anti-frizz effect of our active ingredient. Moreover, it has been described that interaction between HA and keratin in the skin is involved in hydration and skin barrier integrity, we could hypothesise that same interaction in the hair could have benefits on hair structure and further studies should be carried on.
Conclusion: Based on these results, confocal Raman spectroscopy can be considered a powerful and non-invasive technique for investigating the penetration of hair cosmetic ingredients in human hair fibres. To the best of our knowledge, ours is the first study that proves and compare the penetration of different molecular weight hyaluronic acid inside the hair fibres. In this work, we demonstrated that an optimized formulation between different molecular weight HA is able to deeply penetrates the hair cortex to smooth the hair. This insight open new way for the haircare industry to protect and repair human hair using HA.
Methods: Hair locks were irradiated or not with UVA and UVB and then washed with different shampoos. Low molecular weight hyaluronic acid (LMW at 1%), high molecular weight HA (HMW at 1%), or an optimized blend between low and high molecular weight HA (HA-Blend at 1%) were used. A different approach based on confocal Raman spectroscopy has been proposed to track the penetration of active ingredients directly through the human hair fibres. Then, the α-helix/β-sheet ratio of keratin was evaluated by Raman analysis to predict the smoothing effect. At the ex vivo level, photographs were analysed to measure hair strands length before and after four or eight hours in extreme conditions of humidity.
Results: The Raman Z-profile analysis has shown that for the non-irradiated hair locks, there was significantly 5.9 times more HA-Blend than the placebo into the cortex. Besides, the penetration of this optimal HA-Blend was significantly higher compared to the two other actives. Regarding the irradiated hair locks, there was significantly 1.8 times more HA-Blend into the cortex in comparison to the placebo. The HA-Blend significantly penetrated more than the two other actives into the cortex. Whatever the irradiation of the hair locks, no significant difference was obtained for LMW and HMW in comparison to the placebo. Besides, the HA-Blend significantly decreased the α-helix/β-sheet ratio by -10% in comparison to the placebo. We also showed ex vivo that the HA-Blend at 3% significantly decreased the spontaneous frizzing by -11% in comparison to the placebo.
Discussion: For the very first time, we have established an innovative study to prove the penetration of hyaluronic acid inside the hair cortex in rinse-off condition. Irradiation with both UVA and UVB damaged the hair and open cuticle, but only penetration of the HA-Blend was significantly higher than the placebo. Interestingly, even in the non-irradiated condition, the HA-Blend was significantly able to penetrate through the cuticle until the cortex. We have also demonstrated that this optimized HA-Blend decreases α-helix conformation and promotes β-sheet keratin conformation in order to smooth the hair. Thus, we have established that the direct interaction between HA and keratin is responsible for the anti-frizz effect of our active ingredient. Moreover, it has been described that interaction between HA and keratin in the skin is involved in hydration and skin barrier integrity, we could hypothesise that same interaction in the hair could have benefits on hair structure and further studies should be carried on.
Conclusion: Based on these results, confocal Raman spectroscopy can be considered a powerful and non-invasive technique for investigating the penetration of hair cosmetic ingredients in human hair fibres. To the best of our knowledge, ours is the first study that proves and compare the penetration of different molecular weight hyaluronic acid inside the hair fibres. In this work, we demonstrated that an optimized formulation between different molecular weight HA is able to deeply penetrates the hair cortex to smooth the hair. This insight open new way for the haircare industry to protect and repair human hair using HA.