Gilles Genain

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.

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.

Challenging the scalp with ‘dry’ wash shampooing (DW) on Chinese men: an in vivo study

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.