Hair Curl

Your result, the one DNA position behind it, and what the research says.

5/10 confidence.

About Hair Curl

Trichohyalin is a protein that helps set the internal structure of the hair follicle root. What determines whether a strand grows out straight, wavy or curly is the follicle being curved along its length, with a bulb that builds cells faster on one side than the other, so the strand bends as it forms. This position sits outside the gene itself, about sixteen thousand letters past its far end, and is the strongest single contributor to hair curl in European populations. It explains less of the variation elsewhere, where other genes carry more of the difference.

Good to know: Curl comes from the shape of the follicle, not the strand itself. This position is the main curl driver in European ancestry specifically. Hair curl outside Europe is shaped partly by other genes, and this position explains less of the variation there.

Fun fact: A straight follicle grows a straight strand, and the more curved the follicle is along its length, the tighter the curl.

Discovery: The trichohyalin region was linked to hair curl in a study of Australian twins published in 2009.

The Variant

The single variant behind this trait

Gene: TCHH

Variant (rsID): rs17646946

Location: Chr 1:152,090,291

dbSNP rs17646946

The studies

A Comprehensive Review of GWASs of Human Hair Traits (Needle CD et al., The Journal of investigative dermatology, 2025)

Other lifestyle traits

Hair Thickness: A change in a developmental gene that thickens individual hair strands and makes them straighter, alongside a distinctive scooped shape to the front teeth.

Red Hair: Five high-penetrance changes in the MC1R pigment receptor, the main genetic route to red hair and fair, easily burned skin.

Eye Shape and Focus: A variant that nudges how long the eyeball grows, which is what decides whether distant or near objects fall into focus.

Back to All Traits

Content updated September 2026.

ReadYourDNA provides educational interpretation of DNA data you already have. It is not diagnostic, not a substitute for professional medical advice, diagnosis, or treatment, and is not intended to diagnose, treat, cure, or prevent any disease. Talk to a clinician before acting on any result.

Raw DNA Data Reports for 23andMe & AncestryDNA · About ReadYourDNA · FAQ · Methodology & Science · Pricing · Support and complaints · Legal & Contact · Health Traits · Pharmacogenomics · Carrier Status · Variant Explorer · The Human Karyotype · Privacy Policy · Terms of Service · Accessibility · Consumer Health Data Privacy · Your Privacy Choices · Editorial Standards · Your Data, Checkable · Sample Report · ReadYourDNA and Promethease compared · What is inside a 23andMe raw data file · What is inside an AncestryDNA raw data file · What a chatbot can and cannot do with your raw DNA file · Where a raw DNA file can still be uploaded in 2026

Written, maintained and operated by Martin Pechhacker, sole proprietor, Vienna, Austria. Trade register GISA 40064420. support@readyourdna.com