The behavior of hair from different countries.

The properties of curly hair from different countries were assessed using geometrical measurements from a laser scanning micrometer and a new hair shape classification method. In addition, tensile tests, 2-D gel electrophoresis, and differential scanning calorimetry (DSC) were performed. Results concluded that hair characteristics are influenced by the degree of curl. For example, curlier hair tended to be more fragile. Interestingly, the degree of curl in hair also was dependent upon the country of origin. DSC and 2-D gel electrophoresis showed that the thermal behavior and the protein markers in hair differed as a function of hair origin. The variability seen in hair characteristics may potentially influence how the hair responds to treatment and these differences could be caused by regional and cultural diversities in the population from where the hair originated.

Shape variability and classification of human hair: a worldwide approach.

Human hair has been commonly classified according to three conventional ethnic human subgroups, that is, African, Asian, and European. Such broad classification hardly accounts for the high complexity of human biological diversity, resulting from both multiple and past or recent mixed origins. The research reported here is intended to develop a more factual and scientific approach based on physical features of human hair. The aim of the study is dual: (1) to define hair types according to specific shape criteria through objective and simple measurements taken on hairs from 1442 subjects from 18 different countries and (2) to define such hair types without referring to human ethnicity. The driving principle is simple: Because hair can be found in many different human subgroups, defining a straight or a curly hair should provide a more objective approach than a debatable ethnicity-based classification. The proposed method is simple to use and requires the measurement of only three easily accessible descriptors of hair shape: curve diameter (CD), curl index (i), and number of waves (w). This method leads to a worldwide coherent classification of hair in eight well-defined categories. The new hair categories, as described, should be more appropriate and more reliable than conventional standards in cosmetic and forensic sciences. Furthermore, the classification can be useful for testing whether hair shape diversity follows the continuous geographic and historical pattern suggested for human genetic variation or presents major discontinuities between some large human subdivisions, as claimed by earlier classical anthropology.

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. 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.