Validation of hair type diversification for recruiting shampoo panelists without losing data relevance.

A sensory descriptive method is used by the industries to characterize their various products under development. The sensory panelists are recruited through some general criteria suggested in International Standard Sensory Analysis - General guidelines for the selection, training and monitoring of selected assessors and expert sensory assessors [5] but for hair product evaluation, some hair criteria should also be considered, as a major challenge lied in the difficulty to recruit panelists. Such an issue led us to find practical solutions to make this recruitment easier. Among others, one possible solution was to restrict some requirements in the characteristics of hair. This study aimed at checking if a hair type diversification on either sensitization or curliness could influence the sensory perception of shampoos, and, if so, to which extent. This study demonstrates that, for a shampoo trained panel, the evaluation is impacted by the hair curliness but is not impacted by the hair sensitization level.

Une méthode de description des sensations est utilisée par les industries pour caractériser leurs différents produits en cours de développement. Des membres sont recrutés pour un panel en se basant sur certains critères généraux suggérés dans la Norme Internationale d'Analyse sensorielle - Directives générales pour la sélection, la formation et la supervision des évaluateurs sélectionnés et des évaluateurs sensoriels experts [5], mais pour l'évaluation des cheveux, certains critères doivent également être pris en compte, car une des principales difficultés consiste à recruter des panélistes. Ce problème nous a obligé de trouver des solutions pratiques pour faciliter ce recrutement. Entre autres, une solution possible était de limiter certaines exigences au niveau des caractéristiques des cheveux. Cette étude vise à vérifier si la diversité au niveau de la sensibilité ou de la frisure de la chevelure pourrait influencer la perception sensorielle des shampooings, et, si c'est le cas, dans quelle mesure. Cette étude démontre que, pour une palette de 6 shampooings développés, l'évaluation est impactée par la frisure de la chevelure7mais n'est pas impactée par le niveau de sensibilité.

Revisiting, in vivo, the hair regreasing process by the Sebuprint method.

BACKGROUND: The regreasing process of hair by sebum is daily observed by consumers. Methods to investigate this phenomenon were scarcely updated since the 1990s, despite the constant progresses in hair cleaning procedures or shampoo formulations. Our objective was first, to develop an in vivo noninvasive method for quantifying the spread of sebum along the hair shaft. Secondly, we use this new method to define the overall kinetics of the hair-regreasing process among two cohorts of Chinese men with opposite self-perceptions of their scalp/hair greasiness (ie, greasy or not greasy). MATERIAL AND METHODS: One hundred and twenty-three Chinese men (aged 18-35 years) participated to the study. The technique used basically adapts the Sebumeter™ technology where supple polymer films are applied onto and along the hair shaft. The sampled hair sebum is further quantified by image analysis/increased transparency. RESULTS: The technique developed showed an adequate reproducibility under fixed conditions (pressure, investigators, scalp sites, etc.). In the two cohorts of subjects (eg, greasy, nongreasy), hair regreasing process was found sharing a same linear progression with time. The two cohorts of men presented significantly different values in the total amount of spread sebum by an approximately two-fold coefficient, with however comparable average values in the sebum amount present at the root region 48 hours post shampoo. At such timing, the spread of sebum reaches much longer distances in the greasy scalp cohort. CONCLUSION: This technique appears promising for assessing the efficacy of cosmetic ingredients (or products) that aim at delaying a natural process that is daily and negatively perceived by consumers.

The worldwide diversity of scalp seborrhoea, as daily experienced by seven human ethnic groups.

OBJECTIVE: The re-greasing process and kinetics of the human scalp, post-shampooing, have been previously documented, in vivo, on a few Caucasian subjects. The objective of the presented research was to extend such knowledge over seven different ethnic groups. METHODS: The post-shampooing re-greasing kinetics of the scalp was studied on 1325 subjects (women and men of two distinct age classes) from seven different ethnic groups in their residential and native country. Sebum amounts were determined onto small shaved scalp areas at various times post-shampooing, using the Sebumeter® technique. RESULTS: As previously published on Caucasian subjects, scalp re-greasing process follows a hyperbolic-like kinetics over days. However, amounts of collected sebum highly vary with ethnicity. As recorded through the casual level (CL) at the equilibrium phase, 2-3 days post-shampooing, the highest amount of sebum was found in African American subjects, followed in descending order by Caucasian American, Japanese, Chinese, Thai, Caucasian European and Indian subjects, the latter showing very low values. Lower amounts of sebum were recorded in the older age class in all ethnics, as compared to the younger one, and male subjects were found higher sebum producers than women, irrespective of ethnicity. CONCLUSION: The kinetics and slopes of the re-greasing process of the human scalp appear similar in all ethnic groups studied. However, striking quantitative differences are found between the seven ethnic groups, resulting from different sebaceous production levels and scalp hygiene routines.

The diversity of the human hair colour assessed by visual scales and instrumental measurements. A worldwide survey.

OBJECTIVES: To study (i) the diversity of the natural colour of the human hair through both visual assessment of hair tone levels and colorimetric measurements of hair strands collected from 2057 human male and female volunteers, from 23 regions of the world and (ii) the correlation between visual assessments and colorimetric measurements. METHODS: Hair strands were analysed by a spectrocolorimeter under the L*, a*, b* referential system and scored in vivo by experts before sampling, through standardized visual reference scales based on a 1-10 range. RESULTS: Results show that from a typological aspect, black or dark brown hairs largely predominate among studied ethnic groups, whereas Caucasian or derived populations exhibit the widest palette of medium to fair shades, partly explaining some past interbreeding among populations. Instrumental measurements clearly confirm that a given colour of a pigmented hair, at the exclusion of red hairs, is mostly governed by two components, L* and b*, from the L*, a*, b* reference system. CONCLUSION: The comparisons between visual assessments and instrumental data show that these appear closely linked. Darker hairs show close or subtle variations in L*, a*, b* parameters, making their individual colour differentiation calling for technical improvements in colorimetric measurements. The latter are likely governed by other physical factors such as shape, diameter and shine.

What is a Caucasian 'fine' hair? Comparing instrumental measurements, self-perceptions and assessments from hair experts.

OBJECTIVE: To determine the various factors contributing to what Caucasian women describe as 'fine hair'. METHODS: Three complementary approaches were used, namely self-evaluation by the volunteer, assessment by a sensorial expert and instrumental measurements, in order to determine some of the possible parameters taken into account by Caucasian women when they describe the notion of fine hair. One hundred fifty one women of Caucasian origin participated in the study. They varied in age, and varied in that some considered themselves as having fine hair, and others not. The instrumental measurements carried out included hair diameter measurements, hair density measurements, hair breakage force, hair flexibility and scalp sebum levels. RESULTS: From six parameters defined initially, four parameters were found to be in common with the three approaches: hair abundance (density), hair thickness, hair resistance and the volume of the hair on the head. The commonly used term 'body' was only common to self and expert evaluation, whereas the influence of curliness was only common to expert evaluation and instrumental measurements. CONCLUSIONS: This study has shown close agreement between sensorial and instrumental findings, and also illustrates how the women participating can subtly and adequately describe their own hair. It is important to note that the words 'fine hair' describes a lot more than just physically thin hair fibres. Ageing is an additional factor that clearly impacts certain parameters associated with 'fine hair' among the volunteers.

Greying of the human hair: a worldwide survey, revisiting the '50' rule of thumb.

BACKGROUND: While numerous papers have reported on the biological mechanisms of human hair pigmentation and greying, epidemiological descriptions of both natural hair colour and the greying process, worldwide, remain scarce. OBJECTIVES: To assess hair colour and greying in a large world sample of human subjects, and to revisit the validity of the 50/50/50 rule of thumb, which states that 'at age 50 years, 50% of the population has at least 50% grey hair'. METHODS: The natural hair colour of 4192 healthy male and female volunteers was assessed using a sensorial expert evaluation through the comparison of each volunteer's hair with standard swatches. Hair colour was studied according to age, gender and ethnic or geographical origin. RESULTS: Overall we observed that between 45 and 65 years of age, 74% of people were affected by grey hair with a mean intensity of 27%. Men harboured significantly more grey hair than women. Both age at onset and rate of greying with age appeared to be clearly linked to ethnic/geographical origin. Subjects of Asian and African descent showed less grey hair than those of caucasian origin, at comparable ages, confirming previously reported data. CONCLUSIONS: Calculating the percentage of people showing at least 50% grey hair coverage at age 50 years leads to a global range of 6-23%, according to ethnic/geographical origin and natural hair colour: well below that expressed by the '50' rule of thumb.

Age-dependent changes in eumelanin composition in hairs of various ethnic origins.

Hair pigmentation is one of the most conspicuous phenotypes of humans. From a chemical point of view, however, data remain scarce regarding human hair pigmentation characteristics. To determine melanin content and composition in human eumelanic hair from individuals of different ethnic origins and at different ages, we collected hair from 56 subjects with eumelanic hair from each group of African-American, East Asian, and Caucasian origin. The 56 subjects consist of 14, seven each of males and females, each from four age classes of younger than 11, between 12 and 19, between 20 and 45, and older than 46. We analysed hair colour scale, total melanin value, and contents of pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA). We measured age-dependent increases in the relative quantity of eumelanin in pigmented human hairs in the three ethnic groups. Regarding melanin composition, we observed an increase in the PDCA/PTCA ratio with age in African-American and Caucasian hairs until approaching the quite constant level of the ratio in East Asian hairs in the elderly individuals. Our results evidence differences in the content and composition of eumelanin in human hair among African-American, Caucasian and East Asian individuals. Furthermore, we show evidence of age-dependent changes in the quantity and quality of eumelanin in pigmented human hairs. In particular, the age-dependent modification of the PDCA/PTCA ratio, a marker for 5,6-dihydroxyindole units in eumelanin, suggests a chronological evolution of hair follicle melanocyte phenotype (e.g. decrease in dopachrome tautomerase expression).