TLDR Hair diameter and curvature are mostly determined by genetics.
The study measured hair diameter and curvature in 2,332 Australian twins and siblings using an optical fiber diameter analyzer and found that these traits were highly heritable. Genetic factors accounted for 86% of the variance in hair diameter and 53% in curvature for males, and 77% in diameter and 61% in curvature for females. The consistency of hair diameter within individuals was also highly heritable (68%) without sex differences. There were moderate phenotypic correlations between diameter and consistency (r = 0.3) but little correlation between diameter and curvature (r = -0.13). Genetic correlations between hair diameter and consistency were r gF = 0.27 for females and r gM = 0.25 for males.
234 citations,
November 2009 in “American journal of human genetics” Common variants in the Trichohyalin gene are linked to straight hair in Europeans.
479 citations,
January 2005 in “BioEssays” Hair follicle development is controlled by interactions between skin tissues and specific molecular signals.
1113 citations,
August 1999 in “The New England Journal of Medicine” Hair follicle biology advancements may lead to better hair growth disorder treatments.
12 citations,
July 2016 in “British journal of dermatology/British journal of dermatology, Supplement” Different hair fiber development might explain why hair loss severity varies in patients with a specific genetic mutation, and treatments that thicken hair could help.
September 2023 in “Animals” Genes linked to wool fineness in sheep have been identified.
11 citations,
July 2021 in “Genetics selection evolution” Researchers found genes and genetic variants linked to sheep wool and skin wrinkles.
April 2003 in “Experimental Dermatology” The workshop highlighted the genetic links and psychological impacts of hair loss and skin disorders.
Variant G of the KRTAP20-1 gene improves wool curliness in Chinese Tan sheep.
