TESTING
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Figure 3: Subjects with exhibiting increasing degrees of hair greying for determining the linearity of grey hair quantification (on the right: virgin human white hair wig)
female hair from 23 regions of the world8
cosmetic tests. Colour measurements using these
instruments are commonly expressed using the CIE L*a*b* space because of its closeness to the human perception of colours. Luminance L* which measures the lightness from 0 (black) to 100 (white) and b* are the variables of interest (a* is interesting only when blonde-red hair are investigated). Measurements are sometimes performed
directly on the head of the subjects, provided that a reliable repositioning system exists to ensure that measurements are always done on the same location at each kinetics. Yet it is more usual to work on strands of hairs collected by cutting and put in customized sample holders. Indeed, many geometric and physical factors
may impact the measurements. Hair fibres are covered by layers of cuticles which influence the reflection of illuminating light. They also can have different shapes and alignment. Hair fibres heterochromia (mixed colours) add one more level of difficulty. And finally, hair styling can vary during studies. All these heterogeneities and the fact that
chromameter/spectrophotometer probes have small apertures, make it relatively difficult to obtain reproducible and representative data on hair colour. Digital photography is therefore an attractive alternative and has been the most favoured technique these last years. The main advantage is the possibility
to obtain in one single shot an image of a large area. Firstly, this allows one to ‘dilute’ the sources of heterogeneities mentioned previously. Secondly, RGB pixel values can be converted into the L*a*b* colour coordinates familiar to cosmetic scientists.
www.personalcaremagazine.com , or for Several commercial imaging systems are
usable for the accurate quantification of the proportion of grey hair based on colour analysis. In our laboratory, we have decided to develop a method consisting in acquiring photographs of the mid-scalp area of subjects with the handheld Antera 3D® camera (Miravex, Ireland). The associated software can determine the
L*a*b* values. The validation of the technique has been previously reported.9
Briefly, part
of the validation consisted in checking the reproducibility, repeatability and linearity of the method. The latter was done on subjects with different and increasing degrees of greying (Figure 3) and also by introducing various quantities of white hairs to natural ones.
Conclusion Hair greying is a natural phenomenon and almost inevitable for all the persons who have the chance to live long enough. For a long time, camouflage with dyes was the only possible strategy to conceal canities. It is still used as a primary treatment. Now, reversing greying thanks to cosmetic
or pharmacological interventions seems more approachable. The effectiveness of these new treatments will need to be proven. In vitro and ex vivo methods exist for the assessment of hair greying. In this paper, we have focused on in vivo evaluation and quantification methods because of their direct relevance to the substantiation of claims, but the in vitro and ex vivo tools should neither be forgotten nor neglected. Finally, we would like to end with some additional remarks about unpigmented hair. Grey and white hair differ from coloured hair not only by their hue. They exhibit a faster growth, are thicker, have faster water sorption and
desorption. Hair fibres have different physical properties and lipids composition. Therefore, taking care of aged hair should not be restricted to the management of greying.
PC
References 1. Yale K et al. Medication-induced repigmentation of grey hair: A systematic review. Skin Appendage Disorders. 2020; 6, 1–10
2. O’Sullivan JDB et al. The biology of human hair greying. Biological Reviews. 2021; 96, 107-128
3. Tobin DJ. Human hair pigmentation – biological aspects. International Journal of Cosmetic Science. 2008; 30, 233-257
4. Paus R et al. Human hair greying revisited: principles, misconceptions, and key research frontiers. Journal of Investigative Dermatology. 2024; 144, 474-491
5. Trüeb RM. Pharmacologic interventions in aging hair. Clinical Interventions in Aging. 2006; 3, 121-129
6. De Tollenaere M et al. Global repigmentation strategy of grey hair follicles by targeting oxidative stress and stem cells protection. Applied Sciences. 2021; 11(4), 1533
7. Singal A et al. Greying severity score: a useful tool for evaluation of premature canities. Indian Dermatology Online Journal. 2016; 7, 164-167
8. Lozano I et al. The diversity of the human hair colour assessed by visual scales and instrumental measurements. A worldwide survey. International Journal of Cosmetic Science. 2017; 39, 101-107
9. Perin et al. Validation of hair greying measurement using Antera 3D® handheld camera to investigate the effects of treatments for canities. Proceedings of the 32nd IFSCC Congress. 2022
November 2024 PERSONAL CARE
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