TCHH rs1180373: What Your Genotype Means
The rs1180373 variant is a single nucleotide polymorphism located within the TCHH gene. It is statistically associated with variations in hair curliness, wave patterns, and overall hair texture in populations of European descent.
What each genotype means
Increased likelihood of straight hair
You carry two copies of the T allele in the TCHH gene, which has been associated with straight hair texture in populations of European ancestry. Research suggests that this allele influences inner root sheath mechanical strength, slightly reducing hair curliness and wave. Because hair form is complex and polygenic, other genes and environmental treatments also influence your final hair texture.
Found in approximately 15% to 20% of individuals of European ancestry, but virtually absent in East Asian populations.
Intermediate hair wave tendency
You carry one copy of the T allele and one copy of the A allele in the TCHH gene. In European association studies, this heterozygous genotype is typically linked to an intermediate phenotype, contributing to wavy or moderately curled hair patterns. Hair texture is polygenic, so additional variants across other genes also affect whether your hair appears straight, wavy, or curly.
Observed in roughly 45% to 50% of individuals of European ancestry and less common in African and Asian ancestries.
Increased likelihood of curly hair
You carry two copies of the ancestral A allele at this TCHH locus. Studies in populations of European descent associate this genotype with a higher statistical probability of having naturally wavy or curly hair rather than straight hair. Hair morphology is influenced by multiple genes together, so this genotype does not guarantee curly hair on its own.
Carried by roughly 30% to 35% of individuals of European ancestry, and represents the predominant genotype across East Asian and African populations.
Understanding the Variant
The rs1180373 variant is a specific change in the DNA sequence located within the TCHH gene on chromosome 1. In genetics, a single nucleotide polymorphism (SNP) like rs1180373 represents a variation at a single position in the genome. This particular marker has been identified through genome-wide association studies (GWAS) as a potential contributor to the diversity of human hair morphology. While the human genome is remarkably similar across individuals, these small variations help explain why hair texture—ranging from straight to curly—varies so significantly between people. It is important to note that hair traits are polygenic, meaning they are influenced by the combined effects of many different genes and environmental factors, rather than a single genetic switch.
The Role of the TCHH Gene
The TCHH gene provides the instructions for producing a protein called trichohyalin. This protein is essential for the structural integrity of hair follicles, which are the specialized structures in the skin where hair growth begins. Trichohyalin acts as a molecular scaffold, helping to cross-link keratin intermediate filaments within the inner root sheath of the hair follicle. By organizing these filaments, the protein provides the mechanical strength and shape required for the developing hair shaft. When the TCHH gene functions normally, it supports the structural remodeling necessary for healthy hair growth. While rare, severe mutations in this gene can lead to conditions like uncombable hair syndrome, which highlights the critical role this protein plays in determining the physical characteristics of hair.
Research and Evidence
Research into rs1180373 is primarily grounded in studies of European populations. Scientists have observed statistical correlations between this variant and differences in hair curliness and wave patterns. However, the evidence strength for this specific SNP is considered limited. Most studies in this field emphasize that hair morphology is a complex trait influenced by multiple genetic loci, including other genes like EDAR and WNT10A. Because the association between rs1180373 and hair texture is based on population-level statistics, it cannot be used to predict an individual's specific hair type with certainty. Furthermore, these associations are often ancestry-specific; for example, variants that influence hair thickness in East Asian populations may differ entirely from those identified in European cohorts. Current research continues to refine our understanding of how these genetic markers interact with one another.
Population Frequency
The rs1180373 variant is relatively common in populations of European ancestry, with a minor allele frequency (MAF) of approximately 0.42. This means that a significant portion of the European population carries at least one copy of the variant allele. Because it is a common variant, it is considered a normal part of human genetic diversity rather than a rare mutation. Its prevalence suggests that it has been maintained in the gene pool, though its specific evolutionary history and functional impact on hair texture remain subjects of ongoing scientific investigation.
Interpreting Your Information
Information regarding genetic variants like rs1180373 is intended for educational purposes only. It is important to understand that having a specific genotype does not guarantee a particular hair phenotype, as hair texture is influenced by a complex interplay of genetics, hormones, and environmental factors. You cannot use this information to diagnose any medical condition or to predict future health outcomes. If you are interested in learning more about your own genetic makeup, consider consulting with a qualified genetic counselor who can provide context and help you interpret your results accurately. Always remember that genetic markers are just one piece of the puzzle in understanding human biological diversity.
How common is this variant?
The rs1180373 variant is common in European populations, with a minor allele frequency of approximately 0.42.
Frequently asked questions
Does rs1180373 determine if I have curly hair?
No, a single SNP does not determine hair texture. Hair curliness is a complex trait influenced by many genes and environmental factors, and rs1180373 only shows a statistical association with the trait.
Is rs1180373 linked to any health conditions?
While the TCHH gene is associated with uncombable hair syndrome, that condition is caused by rare, severe mutations. The rs1180373 variant is a common polymorphism associated with normal variation in hair texture, not a disease-causing mutation.
Can I change my hair texture based on my genotype?
No, your genotype is fixed at birth. While you can use styling products or treatments to alter the appearance of your hair, your underlying genetic predisposition remains the same.
Why is this variant only associated with Europeans?
Genetic associations often vary by ancestry because different populations have different genetic backgrounds and evolutionary histories. Research on rs1180373 has primarily focused on European cohorts, which is why the association is most documented in that group.
Sources & further reading
Educational information only, last refreshed 10/12/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Common polymorphism in the trichohyalin locus strongly predictive of straight versus curly hair texture morphology in Europeans.
Trichohyalin variant associated with hair curliness in individuals of European descent.
Missense coding variant in trichohyalin that plays a major determinant role in human straight versus curly hair morphology.
This variant in the trichohyalin gene influences hair texture, specifically associated with straight, wavy, or curly hair phenotypes.
Variant in the TCHH gene associated with variation in hair curl structure.
Trichohyalin gene variant associated with straight versus curly hair morphology and texture differences in populations of European descent.