Hair type, encompassing its texture, thickness, and color, is largely determined by an individual’s genetic makeup. While external factors can influence hair’s appearance throughout life, inherited genes provide the fundamental instructions for its development.
Unraveling the Genetic Blueprint of Hair
Hair’s defining characteristics, like straightness, waviness, or curliness, originate within the hair follicle in the skin. The follicle’s shape dictates the hair strand’s cross-sectional shape as it grows. A perfectly round follicle produces straight hair, an oval-shaped follicle produces wavy hair, and a flatter, more elliptical follicle results in curly hair.
Genes also instruct the production and arrangement of keratins, the primary building blocks of hair. These proteins give hair its strength and resilience. Their organization within the hair shaft contributes to its texture and how it bends or coils. Genetic information also influences melanin distribution and type, the pigment responsible for hair color. Eumelanin and pheomelanin are the two main types, determining hair colors from black and brown to red and blonde.
Specific Genes Shaping Your Strands
Research identifies several genes that determine hair characteristics. For example, the TCHH gene (Trichohyalin) provides instructions for a protein in hair follicles that helps form cross-links with keratin intermediate filaments. Variations in TCHH are associated with hair texture, including straightness, waviness, and curliness, particularly in individuals of European ancestry.
EDAR influences hair thickness and straightness, especially in East Asian populations. The FGFR2 gene is also linked to hair thickness, particularly in Asian populations, regulating proteins for hair development. The LIPH gene is involved in hair growth and can affect hair texture, with mutations leading to conditions like woolly hair or sparse hair growth.
Beyond DNA Other Factors at Play
While genetics establish foundational hair type, other factors can influence its appearance and characteristics. Hormonal fluctuations, common during puberty, pregnancy, or menopause, can change hair texture, making it appear thicker, thinner, or altering its curl pattern. For instance, increased estrogen during pregnancy can make hair feel fuller, while its decline postpartum may lead to shedding or texture changes.
Environmental elements, such as humidity or damaging agents, can also impact hair’s look and feel, contributing to frizz or breakage. Medical conditions, including thyroid disorders or autoimmune diseases, along with some medications, can affect hair growth, texture, and lead to hair loss. These influences can modify how genetic predispositions are expressed, but they do not alter the underlying genetic code.
How Hair Type is Passed Down
Hair type is a complex trait, meaning it is influenced by multiple genes, a concept known as polygenic inheritance. Each parent contributes genes to their offspring, and their combination determines the child’s hair characteristics. For instance, while curly hair is considered a dominant trait over straight hair, inheritance is more nuanced, sometimes involving incomplete dominance where a mix of genes results in wavy hair.
Because many genes interact to determine hair type, a child’s hair might not perfectly match that of either parent. A child could inherit a blend of genetic influences, leading to a hair type along a spectrum. Even if both parents have curly hair, they could still have a child with straight or wavy hair due to the complex interaction of multiple alleles and recessive genes. This genetic transmission explains the wide diversity of hair types observed within families and across populations.