The pattern or shape of the hair is influenced by the circumference of the hair, which in turn is determined by the structure of the fiber and its protein composition. Thus, this parameter determines its own characteristics, influences the care or treatment it may need, and affects the ability to maintain its length.
Straight hair is usually fine hair that can easily become greasy and shiny, as oil from the scalp runs down the hair shaft more easily. It is more common in Asians. Naturally wavy hair is usually thicker, usually has waves and the degree of frizziness can be variable. Curly hair appears straight when wet and becomes curly again when dry light and springy. Finally, very curly or kinky hair is usually very thick, with varying degrees of compactness. This is more frequent in people of African descent.
Different studies have observed that this hair structure is determined by the differential organization of the cells of the bulb and the complete fiber of each hair, as well as by the composition and accumulation of keratin and its proteins associated with the hair fiber. In addition, hair shape may also vary with age, among other things because the sebaceous glands of the scalp shrink with time.
Hair shape is a highly heritable trait, and it has been estimated that the heritability of its waviness can be up to 95% in European populations. Based on a GWAS study with a total of 28000 individuals, 9 loci associated to determine hair shape were identified, where we can find genes such as GATA3 or ANXA3.
13.5 million variants
Cloete E et al. Systems Approach to Human Hair Fibers: Interdependence Between Physical, Mechanical, Biochemical and Geometric Properties of Natural Healthy Hair. Front Physiol. 2019; 10:112.
Thibaut S et al. Chronological ageing of human hair keratin fibres. Int J Cosm Sci 2010; 32, 422-434.
Loussouarn G et al. 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. Eur J Dermatol 2016; 26(2): 144-54.
Liu F al. Meta-analysis of genome-wide association studies identifies 8 novel loci involved in shape variation of human head hair. Human Molecular Genetics, 01 Feb 2018, 27(3):559-575.