Geneviève Loussouarn

Ageing and hair cycles

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.

Hair cycle and alopecia.

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.

African hair growth parameters

Background Hair growth parameters have been studied mostly in caucasian hair, whereas few data on African hair have been reported in the literature.

Periodicity in the growth and shedding of hair

Summary 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.

Diversity of hair growth profiles

The appearance of hair differs among the different populations of the world. Do these differences in appearance reflect physiological differences in the growth of the hair? Hair growth parameters have been studied most often in Caucasian hair. 1–9 Very few studies comparing African or Asian and Caucasian hair are available. 10–13 Accordingly, the present work aimed to evaluate and compare the hair growth characteristics of young adult African, Asian and Caucasian volunteers. Although we realize that the classification by ethnologists into these three human groups is wide, each group being likely composed of a complex mosaic pattern, we arbitrarily chose to study hair growth among African people from Central, South and West Africa, Chinese and French people, as “images” of Africa, Asia and Europe, respectively.

Worldwide diversity of hair curliness: a new method of assessment.

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.

Greying of the human hair: a worldwide survey, revisiting the ‘50’ rule of thumb

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.

Pro-Inflammatory Cytokine Cascade in Human Plucked Hair

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 rece

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).

Diversity in human hair growth, diameter, colour and shape. An in vivo study on young adults from 24 different ethnic groups observed in the five continents

BackgroundBased 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.ObjectivesTo measure and compare the hair growth profiles of young adults without alopecia living in the five continents.Materials & Methods2249 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.ResultsDiversity 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.ConclusionOn 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.