A groundbreaking study published in the Journal of Investigative Dermatology has identified the genes that determine the direction of the hair curl. This study not only confirms that the direction of the hair curl depends on genetics, but also shows that it is controlled by several genes. The study, conducted by scientists at the Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences, identified four genetic variants that likely play a role in determining hair curl direction.
Hair curls are sections of hair that grow in a circle around a central point determined by the orientation of hair follicles. They are a prominent feature of an individual and are characterized by the number of curls and the direction of their spiral. Although atypical curls have been observed in people with abnormal neurological development, the genetic basis of these patterns has remained largely unknown.
The study, which is the first genome-wide association study (GWAS) on human scalp hair curls, involved 2,149 Chinese participants from the National Physical Qualities Study. A follow-up study was then conducted on 1,950 Chinese from the Taizhou Longitudinal Study cohort. Through a comprehensive analysis, the scientists were able to identify four genetic variants associated with hair curl direction.
Lead researcher Sijia Wang explains, “Our group studied various interesting appearance traits, and hair curl direction was one of them. The prevailing view was that hair curl direction was controlled by a single gene with Mendelian inheritance. However, our results show that it is actually influenced by the combined action of several genes, suggesting polygenic inheritance.”
The identified genetic variants are located in specific regions of the genome (7p21.3, 5q33.2, 7q33 and 14q32.13) and likely regulate the cell polarity of hair follicles, which in turn affects the direction of the hair curl. The study also suggests that cranial neural tube closure and growth may play a role in this process.
Although previous studies have suggested an association between hair coil direction and abnormalities of neurodevelopment, this study found no significant genetic associations between hair coil direction and behavioral, cognitive, or neurological phenotypes. However, the researchers believe that further studies are needed to fully understand the complex genetic mechanisms underlying external traits.
Prof. Wang concludes: “Although we still have much to learn about why we look the way we look, our curiosity will undoubtedly lead us to answers. This study represents an important step towards unraveling the genetic basis of hair coil direction and sheds light on the complex processes involved in human development.”
