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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.

Based on previous findings, from a worldwide study, classified the shapes of human hair into 8 major types, from straight to highly curly. This clearly extended the usual classification of hair into African, Asian or Caucasian types. However, determinations of hair growth parameters and hair density were excluded from such studies. To measure and compare the hair growth profiles of young adults without alopecia living in the five continents. 2249 young adults (18-35 years, females and males) without alopecia, originating from 24 various human ethnic groups were included in the study. Total hair density, telogen percentage and growth rate on three different scalp areas were measured, using non-invasive validated techniques. Natural hair colour level, curliness and hair diameter were additionally recorded, when practically possible. Diversity in hair growth parameters among the entire cohort was a key finding, with differences linked to scalp area, gender and geographic origin. Statistical approaches depicted African hair as having lower density and a slower growth rate. Asian hair showed a thicker diameter, with faster growth. Caucasian hair showed a high total hair density. On the one hand, this inter-continental study of hair growth parameters provides initial valuable base-line data on hair in young adults without alopecia, and on the other hand, further extends our knowledge of this unique human appendage, with some mosaic features, observed worldwide.

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.

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.

Synopsis 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).

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.

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.

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.

Skin ageing and gender influences on the scalp have been seldom studied. We revisited the changes in the interfollicular scalp. The study was performed on a population of 650 volunteers (300 women and 350 men) for over 7 years. Three age groups were selected in both genders, namely, subjects aged 20–35, 50–60, and 60–70 years. The hair status was further considered according to nonalopecic and alopecic patterns and severity (discrete, moderate, and severe). Biopsies from the parietal area were processed for immunohistochemistry. Stromal cells were distinguished according to the presence of vimentin, Factor XIIIa, CD117, and versican. Blood and lymphatic vessels were highlighted by Ulex europaeus agglutinin-1 and human podoplanin immunoreactivities, respectively. Actinic elastosis was identified by the lysozyme coating of elastic fibres. The epidermis was explored using the CD44 variant 3 and Ki67 immunolabellings. Biplot analyses were performed. Immunohistochemistry revealed a prominent gender effect in young adults. Both Factor XIIIa+ dermal dendrocytes and the microvasculature size decreased with scalp ageing. Alopecia changes mimicked stress-induced premature senescence.

Cosmetic habits show a strong diversity worldwide. The same applies to procedures that are considered as basic hygiene acts such as shampooing. Apart from common traditional shampoo routine, a special shampoo procedure, 'dry' wash is daily performed in Chinese hair salons. Without pre-wetting step, hairdresser applies the shampoo directly to dry hair with small quantity of water to create foam. Hand massaging is then offered on the scalp. This shampooing process is distinguished from traditional 'regular wash' by slightly diluted shampoo, and longer contact with the scalp and scalp massaging, all of which could be possibly considered as challenges to the structure and barrier function of the scalp. In this study, the effects of 'dry' wash on Chinese scalp have been investigated, in vivo, using regular wash as a control. A total of 67 Chinese males in two cohorts, non-dandruff and with dandruff, were included. In each cohort, volunteers were split into two groups, one with 'dry' wash and the other one with regular wash. Both shampoo methods were performed daily for five consecutive days using the same shampoo formulation. Volunteers' self assessment, clinical assessment by an expert and instrumental measurements were carried out. The results showed that Chinese 'dry' wash did not induce any negative consequence on the scalp physiology under such experimental conditions.

Synopsis Chronobiology governing the hair cycle is a fascinating and complex process. Both the hair growth cycle and the hair shaft growth are coordinated and depend on the interplay of different biological signals and various exogenous stimuli. A latency period may occur between hair shedding (teloptosis, exogen phase) and the early emergence of the next anagen VI stage. This lag time referred to on the hair eclipse phenomenon likely depends on the influence of a series of distinct synchronizers, and does not represent per se a peculiar hair cycle phase. It is the result of some dysregulations of the hair cycling, involving early teloptosis, delayed anagen I initiation or stunted hair growth at any stage between the anagen I and anagen V phases. As such, the hair eclipse phenomenon may be an erratic process occurring in physiopathological conditions affecting hair follicles singly or in focal to generalized patterns. It may be more frequent when it follows synchronized teloptosis occurring in telogen effluvium (newborn alopecia, post-partum alopecia, seasonal alopecia and alopecia areata). It may also be prominent when microinflammation is abutted on the permanent portion of the hair follicle as in dandruff, seborrhoeic dermatitis, androgenic alopecia and photoageing baldness. Local synchronizers such as growth factors and other mediators may eventually be lacking or involved in the hair eclipse phenomenon. Their identification and characterization might drive new corrective or preventive applications. Resume La chronobiologie a la source du cycle pilaire est un processus a la fois complexe et fascinant. Le cycle pilaire et la croissance pilaire sont coordonnes et dependent de l'interaction de divers signaux biologiques et stimuli exogenes. Un temps de latence peut survenir entre la chute du cheveu (teloptose, phase ‘exogene’) et l'emergence du cheveu suivant en stade anagene VI. Cette periode correspondant au phenomene d'eclipse pilaire est sous l'influence probable d'un ensemble de synchronisateurs distincts et ne represente pas en tant que tel une phase particuliere du cycle pilaire. Ce phenomene serait en fait le resultat de deregulations du cycle pilaire impliquant une teloptose precoce, un retard d'initiation du stade anagene I, ou un arret transitoire de croissance pilaire a n'importe quel moment entre les stades anagenes I et V. Le phenomene d'eclipse pilaire peut donc etre un processus erratique survenant dans diverses situations physiopathologiques atteignant des follicules pileux isoles, groupes focalement ou disperses de maniere generalisee. Il peut etre plus frequent a la suite d'une teloptose synchronisee a l'origine d'un effluvium telogene (alopecie du nouveau-ne, alopecie du postpartum, aloepcie saisonniere, pelade). Le phenomene d'eclipse pilaire peut egalemnet etre important lorsqu'une microinflammation entoure la portion permanente du follicule pileux. Tel est le cas dans les etats pelliculaires, la dermite seborrheique, l'alopecie androgenetique et l'alopecie du photovieillissement. Des synchronisateurs locaux tels que des facteurs de croissance et d'autres mediateurs pourraient etre deficients ou au contraire etre impliques dans le phenomene d'eclipse pilaire. Leur identification et caracterisation pourraient aboutir a des applications a visee corrective ou preventive.

Dandruff is known to be controlled by fungistatic shampoos active against Malassezia spp. These products also remove the loosely attached scales. This study was performed to assess the effect of a 5-min residence time on the efficacy of antidandruff shampoos. Two commercially available shampoos were used in two groups of 21 panelists with severe dandruff. They contained either 1% ketoconazole or 1% piroctone olamine. In each group, intraindividual comparisons were made by a split-scalp design between the effect of a 5-min residence time versus no residence time. Both shampoos induced significant reductions in scaliness and yeast colonization. The beneficial effects were obvious immediately after one single shampooing and 3 days later as well. The improvement was greater with a 5-min residence time. The piroctone olamine treatment benefited more than the ketoconazole treatment from the extension of shampoo-exposure time. In conclusion, the benefit of a residence time in treating dandruff is documented. The level of improvement in efficacy may vary according to the nature of the shampoo.

Background For many years, cosmetic scientists have attempted to measure the physical features of human hair, such as its shape and colour, as these can be artificially modified using cosmetic products. With regard to hair shape, previous anthropologic studies have emphasized its variability within and between human ethnic groups. Many studies have broadly distinguished three ethnic human subgroups: African, Asian, and Caucasian. Such a broad classification cannot account for the great complexity of human biological diversity, resulting from multiple, past or recent mixed origins. The verbal description of hair shape ranges from the classic to the more sophisticated, with terms such as straight, wavy, curly, frizzy, kinky, woolly, helical, etc. Although these descriptions evoke a global appearance, they remain confusing as their definitions and limits are unclear. Assessments are therefore required to more accurately define such verbal attributes. Objective The work reported here attempts to address the following issues: (i) to define hair types according to specific shape criteria through objective and simple measurements; and (ii) to define such hair types without referring to human ethnicity. Methods Measurements of four parameters related to hair curliness (curve diameter, curl index) or kinking of the hair (numbers of waves, numbers of twists) were performed on hair from 2449 subjects from 22 different countries. Principal components analysis and hierarchical ascendant classification were used to identify homogeneous groups of hair and to determine key variables for the assignment of group membership. Finally, a segmentation tree was prepared in order to establish simple rules for predicting group membership of new subjects. Results and conclusions This study has shown that it is possible to classify the various hair types found worldwide into eight main groups. The approach involves objective descriptors of hair shape, and is more reliable than traditional methods relying on categories such as curly, wavy, and kinky. Applied to worldwide human diversity, it avoids reference to the putative, unclear ethnic origin of subjects. Briefly, a straight hair type I is just that, and whether it originates from a Caucasian or an Asian subject is not at issue. The hair types defined here also more adequately reflect the large variation of hair shape diversity around the world, and may possibly help to trace past mixed origins amongst human subgroups.

Summary Background. In some individuals, dandruff may be recurrent and even chronic. This represents a difficult-to-treat condition. Excessive hair shedding and diffuse alopecia may develop. Objectives. To evaluate the chronobiological aspects of dandruff, hair shedding and alopecia. Methods. This study was performed in eight men suffering from such a scalp condition. They were examined 40 times at regular intervals for five consecutive years. Hair-density assessments and trichograms were performed at least twice per trimester on the parietal region of the scalp, corresponding to an area where dandruff was present. Results. A positive correlation was found between the percentage of telogen hairs and dandruff severity as assessed by the squamometry index. Bimodal yearly biorhythms were found for dandruff severity, telogen counts and hair loss between two consecutive visits. The chronobiological fluctuations were prominent in some study participants, but remained inconspicuous in others. The biorhythms were almost synchronized in all participants, showing variations over the year. Conclusions. The biorhythms on the hair cycle in dandruff are not fundamentally different from those previously reported in subjects without dandruff. The periodicity may be an intrinsic feature of human skin.

Based on the clinical presentation of some skin pigmentation disorders it is thought that a bicompartmental functional system exists in the epidermal melanocyte population. It corresponds to the perifollicular and interfollicular compartments, respectively. The present study was undertaken looking for the presence of such a system on scalp unaffected by pigmentary disorders. The scalps of 100 men with incipient to severe androgenic alopecia were examined using a videocamera equipped with an internal ultraviolet light-emitting unit. The face, trunk and limbs were similarly examined in 45 of these adults and in 13 children of both sexes. In 92 men, a subclinical hypermelanosis was found as a speckled pattern centered on every single follicle. With increasing baldness severity, another epidermal hyperpigmentation pattern involving the interfollicular area was superimposed to the perifollicular pattern. These stereotyped patterns of subclinical melanoderma were also disclosed on the face of adults, but not in children. In addition, the spotty perifollicular pattern was discrete or not apparent on the other parts of the body. It is concluded that the perifollicular subclinical melanotic pattern is a regional characteristic of cephalic skin, perhaps related to the local production of melanocortins, particularly alpha-MSH by the pilosebaceous unit.

The hair follicle cycle successively goes through the anagen, catagen, telogen, and latency phases, which correspond, respectively, to hair growth, arrest, shedding, and absence before a new anagen phase is initiated. Experimental observations collected over a period of 14 years in a group of 10 male volunteers, alopecic and nonalopecic, allowed us to determine the characteristics of scalp hair follicle cycles. On the basis of these observations, we propose a follicular automaton model to simulate the dynamics of human hair cycles. The automaton model is defined by a set of rules that govern the stochastic transitions of each follicle between the successive states anagen, telogen, and latency, and the subsequent return to anagen. The transitions occur independently for each follicle, after time intervals given stochastically by a distribution characterized by a mean and a variance. The follicular automaton model accounts both for the dynamical transitions observed in a single follicle and for the behavior of an ensemble of independently cycling follicles. Thus, the model successfully reproduces the evolution of the fractions of follicle populations in each of the three phases, which fluctuate around steady-state or slowly drifting values. We apply the follicular automaton model to the study of spatial patterns of follicular growth that result from a spatially heterogeneous distribution of parameters such as the mean duration of anagen phase. When considering that follicles die or miniaturize after going through a critical number of successive cycles, the model can reproduce the evolution to hair patterns similar to well known types of diffuse or androgenetic alopecia.

Using reverse transcriptase polymerase chain reaction we showed that freshly plucked human anagen hair expressed both type 1 (80 kD) and type 2 (60 kD) interleukin (IL)-1 receptor mRNAs. The IL-1 receptor type 1 was functional since after in vitro stimulation of plucked hair with IL-1Α, we observed the induction of mRNA(s) for the inflammatory cytokines IL-1Β, tumour necrosis factor Α and IL-6 as well as for the chemokines monocyte chemotactic and activating factor and IL-8. In addition, the growth of dissected human anagen hairs in culture in vitro was significantly and dose-depen-dently inhibited by IL-1Α as a consequence of hair bulb degradation. These observations, together with those of other authors in IL-1Α transgenic mice evidence the inhibitory role of IL-1 on human hair growth. Therefore, in order to identify individuals with high inflammatory potential in their hair follicle environment, we designed a rapid and simple assay to detect variations in the level of IL-1Α production in the overnight supernatant of plucked hairs in culture. We observed that 32.7% of the specimens from the volunteers tested (n = 116) could be considered highly inflammatory in terms of IL-1Α production. Altogether, these results suggest that in alopecia androgenetica, hair growth might be negatively influenced by IL-1, directly produced by the outer root sheath keratinocytes. Consequently, identifying the ‘inflammatory alopecic individual’ might be of clinical interest to discriminate among individuals for whom anti-IL-1 strategies might be of therapeutic relevance.

The phototrichogram is a non-invasive technique by which, on the same precise area of the scalp, each individual hair may be identified, and its current growth phase established. This technique was used to study the duration of hair cycles in 10 male subjects, balding and non-balding, by observations at monthly intervals over a period of 8-14 years. The accumulated data served to characterize the effects of ageing in these subjects: a reduction in the duration of hair growth and in the diameter of hair shafts, most evident in the thickest hairs, and a prolongation of the interval separating the loss of a hair in telogen and the emergence of a replacement hair in anagen. These various aspects of ageing of scalp hair contribute to its progressive overall impoverishment. They resemble those observed in the course of male-pattern balding, although their development is less marked.

Male pattern alopecia is the outcome of profound modifications in the duration, succession and frequency of hair cycles. These phenomena were studied by phototrichogram in 10 male subjects, with or without alopecia, over a period of 15 years. Almost 10,000 hair cycles were accounted for, yielding a detailed picture of the alopecia condition: (1) A decrease in the duration of anagen for a certain proportion of hairs, a proportion which increases in size, the more advanced the alopecia; the result of this premature transformation from anagen to telogen is an increase in the rate of hair loss. (2) A parallel decline in hair diameter. (3) Longer latency periods between the fall of a hair and the onset of regrowth, leading to a reduction in the number of hairs present on the scalp surface. The shorter finer hairs are absent more frequently and absent for longer periods and this contributes to the effect of alopecia.