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Objective To determine, in vivo, the density, growth rate and percentage of anagen phase follicles of body hairs present on five different skin sites (axilla, cheek, chin, leg, upper-lip) of women and men from four different ethnics (African, Caucasian, Chinese, North African). The same characteristics of terminal hairs from the nape of all subjects were recorded as references. Methods The photo-trichogram technique was used on all skin sites (of different sizes) at variable times (2 or 3 days) post shaving of small skin areas (a few cm2 ). Digital photographs were then analysed through a dedicated software that allows to record the density of body hairs (N cm-2 ), the % of growing hairs (Anagen phase) and their growth rates (in μm day-1 ). Results The densities of terminal hairs (on nape) found on all subjects were similar to those previously observed on much larger populations. The same ranking of a decreased density of body hairs in the five skin sites was observed in men, irrespective with ethnics. Body hairs seem homogeneously distributed among ethnics on armpit and leg with slight gender-related differences. In men, a significantly higher anagen phase percentage (> 85%) is found on terminal hairs, cheek and upper-lip region in Caucasians and North Africans, as compared to African and Chinese men. The technique used cannot precisely determine the very thin hairs present on the faces of all women. The anagen phase percentage appears higher in all women on leg and armpit. Hair body growth rates ranged from 180 to 485 μm day-1 and were found, on axilla, close to those of terminal hairs. Conclusion The abundance of body hairs, in the studied skin sites, appears similar, irrespective with ethnic groups, whereas their functional characteristics (anagen ratio, growth rate) are more driven by individual/gender influences. RESUME: Objectif Determiner, in vivo, la densite, la vitesse de pousse et le pourcentage de follicules en phase anagenes des poils corporels presents sur 5 sites cutanes differents (l'aisselle, la joue, le menton, la jambe, la levre superieure) de femmes et d'hommes issus de 4 groupes ethniques differents (Africain, Caucasien, Chinois, Nord-africain). Ces memes caracteristiques ont ete enregistrees pour les cheveux (poils terminaux) en nuque de tous les sujets en tant que references. Methodes la technique du photo-trichogramme a ete utilisee sur tous les sites cutanes (de tailles differentes) apres un temps variable (2 ou 3 jours) suivant le rasage de petites zones cutanees (quelques cm-2 ). Les photographies numeriques ont ete alors analysees par un logiciel specifique qui permet d'enregistrer la densite de poils corporels (N.cm-2 ), le pourcentage de poils en phase de croissance (la phase Anagene) et leur vitesse de pousse (en µm/jour). Resultats la densite de cheveux (en nuque) trouvee sur tous les sujets etait semblable a celle precedemment observee sur des populations beaucoup plus larges. On retrouve chez les hommes le meme classement entre les 5 sites cutanes en termes de densite de poils corporels, independamment du groupe ethnique etudie. Les poils corporels semblent distribues de maniere homogene parmi les membres d'un groupe ethnique sur l'aisselle et la jambe avec des legeres differences liees au genre. Chez les hommes, les Caucasiens et les Nord-Africains presentent un pourcentage de poils terminaux en phase anagene significativement plus eleve (>85%) sur la joue et la region de la levre superieure que les hommes Africains et Chinois. La technique utilisee ne permet pas precisement de determiner la presence de poils tres minces sur les visages des femmes. Le pourcentage de poils en phase anagene parait plus eleve chez les femmes sur la jambe et l'aisselle. Les vitesses de pousse des poils corporels s'etendent de 180 a 485 µm/jours et se trouvent, sur les aisselles, proches de celles des cheveux. Conclusion la densite de poils corporels, dans les sites cutanes etudies, presente une variabilite de sites independante du groupe ethnique considere, tandis que leurs caracteristiques fonctionnelles (le ratio de poils en phase anagene, la vitesse de pousse) sont plus dirigees par des influences d'individu/genre.

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.

Summary 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.

Biological rhythms are numerous and vary according to periodicity and amplitude. Variations over the course of a day, particularly circadian rhythms have been reported in the skin of the face and forearms. However, little information is available about daily biorhythms of the scalp. The aim of the present study was to explore the chronophysiology of the scalp. We report a series of diurnal rhythms in 8 Caucasian men using the plexogram method at 4-h intervals over a 5-day period. Statistically significant biorhythms were found for the colour, hydration, barrier function and pH of the skin, and for the sebum excretion as well. The early afternoon was the time of maximum increase in redness, hydration, pH and sebum output, combined with decreased skin barrier function. The amplitude of some of these biorhythms was so discrete that their clinical relevance remained uncertain even when they appeared statistically significant. In view of the apparent synchronization between them, it is likely that a central oscillator exerts a major influence. However, only rare subjects exhibited biorhythms for all the considered physiological parameters. Hence, peripheral reactivity and/or environmental synchronizers also play an important role to define the good and bad respondors to the potential biorhythms of each individual parameter.

Silicon image sensor (SIS) technology was recently introduced as an innovative tool (SkinChip®, L'Oreal) providing sensitive imaging of the skin capacitance. This method can detect discrete focal variations in skin surface hydration, and thus early discrete manifestations of skin irritation induced by surfactants. In the present in vivo study, 2 neat and diluted shampoos, and 5% and 10% sodium laurylsulfate solutions were tested on human skin. Each surfactant solution was gently rubbed on the skin using wet hair wicks mimicking the casual use of a shampoo on the scalp. Clinical and SIS evaluations were carried out. In addition, the same products were tested using the ex vivo corneosurfametry bioassay performed on human stratum corneum (SC) harvested by cyanoacrylate skin surface strippings. The colourimetric index of mildness (CIM) was measured on these samples. The product reactivity with the SC was recognized by darker skin capacitance images, and by both lowered SkinChip®-generated values and lowered CIM values. The extent in changes varied according to the nature of the test products and their concentrations. The SkinChip® image changes likely corresponded to the acute surfactant-induced water swelling of the corneocytes. Skin capacitance imaging and corneosurfametry allow to disclose discrete surfactant-induced alterations of corneocytes.

Human scalp hair consists of a set of about 10(5)follicles which progress independently through developmental cycles. Each hair follicle successively goes through the anagen (A), catagen (C), telogen (T) and latency (L) phases that correspond, respectively, to growth, arrest and hair shedding before a new anagen phase is initiated. Long-term experimental observations in a group of ten male, alopecic and non-alopecic volunteers allowed determination of the characteristics of hair follicle cycles. On the basis of these observations, we previously proposed a follicular automaton model to simulate the dynamics of human hair cycles and the development of different patterns of alopecia [Halloy et al. (2000) Proc. Natl Acad. Sci. U.S.A.97, 8328-8333]. The automaton model is defined by a set of rules that govern the stochastic transitions of each follicle between the successive states A, T, L and the subsequent return to A. These transitions occur independently for each follicle, after time intervals given stochastically by a distribution characterized by a mean and a standard deviation. The follicular automaton model was shown to account both for the dynamical transitions observed in a single follicle, and for the behaviour of an ensemble of independently cycling follicles. Here, we extend these results and investigate additional properties of the model. We present a deterministic version of the follicular automaton. We show that numerical simulations of the stochastic version of the automaton yield steady-state level of follicles in the different phases which approach the levels predicted by the deterministic equations as the number of follicles progressively increases. Only the stochastic version can successfully reproduce the fluctuations of the fractions of follicles in each of the three phases, observed in small follicle populations. When the standard deviation is reduced or when the follicles become otherwise synchronized, e.g. by a periodic external signal inducing the transition of anagen follicles into telogen phase, large-amplitude oscillations occur in the fractions of follicles in the three phases. These oscillations are not observed in humans but are reminiscent of the phenomenon of moulting observed in a number of mammalian species.

Synopsis Objective To confirm the existence of seasonal hair growth cycle among Chinese subjects and objectivize the seasonal effect of hair loss; the hair growth parameters of Chinese volunteers were followed monthly for an entire year on the same area of vertex. Methods The hair growth parameters of 41 Chinese volunteers (women and men), free from alopecia, were recorded monthly along an entire year using the phototrichogram technique. Results Results show an increased rate of telogen hairs (growing arrest) around August–September in the study group, as previously reported in European subjects albeit of a lower extent and remaining within the normal range of healthy head hair parameters. The possible effects of latitude and daylight duration are discussed. Conclusion Data confirm that Chinese hairs present characteristics of the most developed and fast growing terminal fibres, as compared to other non-Asian ethnics. Resume Objectif Afin de confirmer l'existence d'un effet de saisonnalite au sein des cycles de croissance et de chute des cheveux chez des sujets Chinois, les differents parametres de ces cycles sur une meme region du vertex, ont ete observes chaque mois durant une annee entiere. Methodes les parametres de croissance des cheveux de 41 volontaires Chinois (femmes et hommes), non-alopeciques, ont ete determines chaque mois au long d'une annee entiere, par la technique du Phototrichogramme. Resultats L'etude montre, comme chez les sujets Europeens, une augmentation du taux de cheveux en phase Telogene (arret de croissance) vers Aout-Septembre, mais d'une plus faible amplitude chez les sujets Chinois, de valeur demeurant dans l'etendue des variations d'une chevelure normale en bonne sante. Les effets possibles de la latitude et des cycles jours-nuits sont discutes. Conclusion Les resultats confirment aussi que les Cheveux Chinois presentent toutes les caracteristiques de forte croissance de follicules pileux les plus developpes, compares aux autres ethnies non Asiatiques.

Background Hair growth parameters have been studied mostly in caucasian hair, whereas few data on African hair have been reported in the literature. Objectives To evaluate hair growth characteristics of African volunteers born in Africa. Methods Thirty-eight young adults (19 women, 19 men, mean +/- SD age 27 +/- 10 years), native of central and western Africa, took part in the study. Phototrichograms were performed in order to record three parameters of hair growth: hair density, telogen percentage and rate of growth. For each volunteer, three regions of the scalp, namely vertex, temporal and occipital areas, were assessed. Results Hair density varied from 90 to 290 hairs cm(-2), with higher counts on the vertex. No significant difference between men and women was recorded. Telogen percentage showed wide variations, from 2 to 46%, with higher levels on the temporal area and in men. The rate of growth fluctuated from 150 to 363 microm day(-1) with no difference related either to gender or to scalp region. These data were compared with those previously obtained in caucasian volunteers of comparable age, and showed significant differences between the two ethnic groups in all three parameters studied. Hair density in African volunteers was lower than that in caucasians (mean +/- SD 190 +/- 40 and 227 +/- 55 hairs cm(-2), respectively). African hair grew at a much slower rate than caucasian hair (mean +/- SD 256 +/- 44 vs. 396 +/- 55 microm day(-1)), and telogen counts were frequently higher in African hair (mean +/- SD 18 +/- 9% vs. 14 +/- 11%). Conclusions This study demonstrated significant differences between African and caucasian hair growth parameters, which might suggest a trend towards increased hair loss in Africans, even though it contrasts with a lower and slower incidence of the development of alopecia in Africans.

Ten men, with or without alopecia, were observed for a period of between 8 and 14 years using phototrichograms on a precisely located zone on the vertex of the scalp. Among the various parameters observed, we chose the percentage of hairs in telogen as the criterion for assessment of hair shedding. Mathematical analysis of the variations in this telogen percentage was carried out for each individual subject and for the whole group, as represented by the population mean (or the 'average subject'). This analysis demonstrated the existence of overall annual periodicity, manifested by a maximal proportion of telogen hairs at the end of summer and the beginning of autumn. Some subjects also exhibited a periodicity approximately corresponding to two annual peaks. In those subjects with a very low proportion of hairs in telogen, no periodicity was demonstrated. In another group of subjects, it has been shown that the variations in telogen percentage reflect those observed in hair shedding, assessed in a standardized manner. Periodicity of the telogen percentage, and hence of hair fall, is not independent of climatic factors (sunshine hours), and these must be taken into account when assessing the treatment or prevention of hair loss.

Background Ageing of the skin, being chronological or sun induced is highly documented. Scalp, as a specific skin site, has, however, received little attention. This work attempted to describe functional and structural alterations that occur in scalp skin with ageing. Methods Two different age groups (N = 15 each; 30 ± 3 and 62 ± 2 y.o. respectively) of Caucasian women participated in the study. Some functional parameters (TEWL, Sebum level, Hydration, T°) were recorded on the vertex part of the scalp, after having cut the hair flat on the scalp surface. Imaging of some structural criteria was carried out using high-frequency ultrasound technique and optical coherence tomography on the same scalp site and on the mid-forehead, as a close control skin site. Results As compared with the younger group, the scalp of older women significantly showed a decreased TEWL and a slightly lower T°. The thickness of total skin (epidermis + dermis) increased with age on both scalp and on forehead. The thickness of scalp epidermis decreased with age while not significantly altered on forehead. Pseudoattenuation of ultrasound images increased in the older age group. Other criteria, such as sebum level, stratum corneum hydration, stratum corneum thickness, were not found altered with age. Conclusion With ageing, some few functional and structural changes are observed in the scalp of Caucasian women. Similarities or differences with those previously reported in other skin sites are discussed.