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.

Changes in Chinese hair growth along a full year.

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.

Relationships between hair growth rate and morphological parameters of human straight hair: a same law above ethnical origins?

After measurement of individual growth rates, natural hair fibres from Asian and Caucasian subjects were analysed using scanning electron microscopy. In total, more than 1000 hairs were analysed. Measurements of diameter, medulla and interscale distance (average distance between two successive cuticle scales) show these parameters strongly correlated with hair growth rate. A thicker hair fibre corresponds to a faster growth rate, a shorter interscale distance and greater probability to have a medulla, and vice versa, a thin hair fibre shows slower growth rate, a larger interscale distance and a lower probability to have a medulla. Very interestingly, this finding appears to be unrelated to the ethnic origin of the subjects, suggesting a common characteristic of human hair, at least for the straight or semi-straight hair studied. From a practical viewpoint, this finding clearly suggests an alternative method for measuring hair growth rates, by measuring the interscale distance, which appears easier than using common laboratory equipments.

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.