Hair texture has often been described by many scientific authors in terms of three racial types: African, Caucasian, and Asian. However, it has been noted that there is significant intra-racial variation, with scientists now suggesting that hair be described by its degree of curliness with a broad definition of straight, wavy and curly. In general, the degree of curliness correlates with the distribution of hair keratins and cell type within the hair fiber, as well as with the number of mesocortical cells. The curlier the hair, the fewer mesocortical cells are present. See this past post on the distribution of cells affecting the hair texture:
http://askthehairdoc.com/the-hair-shaft/
Embarking on this mission, scientists collected hairs from almost 1500 subjects located in eighteen countries worldwide. Persons were not to have a perm, straightener, or relaxer in their hair. Hairs were taken from the vertex, nape, and temples. Four parameters were used to type the hairs, namely Curl Diameter, Curl index (ratio of stretched length of hair to length at rest), highest number of waves and the highest number of constrictions. Based on their findings, they devised a hair typing system as depicted in the figure below. The experiment was repeated on a larger scale thus validating the results.
Hair Texture Typing Photo Scale
Source: de la Mettrie R, Saint-Leger D, Loussouarn G et al. Shape variability and classification of human hair: A worldwide approach. Human Biology 2007; 79: 265-81.
Other genetic studies have been done showing why certain populations have specific hair types. East Asians were found to have the mutation in the gene for the ectodysplasin A receptor (EDAR) and the FGFR2 gene polymorphisms. These two genes are associated with the thickness of hair. The positive selection in this group resulted in hair being thicker than all other races. In Europeans, variations of the gene coding for the Trichohyalin protein were found to be responsible for the development of straight, wavy or curly hair, with Northern Europeans having the highest variation.
The Hair Doc
Dr. Llorenia Muir-Green is a practising dermatologist in Jamaica. She has an avid interest in hair and scalp disorders. She is a member of the Medical Association of Jamaica, Dermatology Association of Jamaica and is an Associate Member of the Caribbean Dermatology Association. She was a recipient of the 2013 Fellowship in Hair and Scalp Disorders at the University of British Columbia.
