What you carry at this position in your DNA and what research says about it.
Estrogen and Hair Health: 7/10 evidence, 35 publications.
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Sample genotype (not yours): A/A
Lower Hair Loss and Migraine Risk
This genotype is associated with lower susceptibility to female pattern hair loss and migraines. It may also lead to a highly variable response to certain hormone therapies.
What this genotype means: Lower risk of female pattern hair loss; Reduced susceptibility to migraines; Variable response to breast cancer endocrine therapies.
Sample genotype (not yours): A/C
Better Hormone Therapy Response and Lower Migraine Risk
This genotype is linked to an improved response to tamoxifen hormone therapy and a lower risk of migraines. Hair loss risk remains at a typical baseline level.
What this genotype means: Improved response to tamoxifen therapy; Lower susceptibility to migraines; Typical risk of female pattern hair loss.
Sample genotype (not yours): C/C
Higher Risk of Female Pattern Hair Loss
This genotype is associated with an increased risk of female pattern hair loss. It also represents a typical baseline for migraine susceptibility and hormone therapy response.
What this genotype means: Increased risk of female pattern hair loss; Typical baseline susceptibility to migraines; Standard response to breast cancer hormone therapies.
Gene function and biological role
Gene Function: The CYP19A1 gene encodes aromatase, the key enzyme responsible for the final step in estrogen biosynthesis, converting androgens like testosterone into estrogens [1]. This enzyme is highly active in ovaries, adipose tissue, the brain, and hair follicles [2]. Variations in this gene can alter circulating estrogen levels and influence hormone-sensitive tissues throughout the body [1]. Because estrogens can stimulate the growth of hormone receptor-positive breast tumors, this gene is a major focus in breast cancer research and endocrine therapy [3].
Variant Impact: The rs4646 variant is a single nucleotide polymorphism located in the 3 prime untranslated region of the CYP19A1 gene, a region critical for regulating gene expression [4]. This genetic change is thought to affect the stability or translation of aromatase messenger RNA, thereby modulating enzyme activity and estrogen levels [2]. The C allele is the more common version globally, while the A allele is less frequent. Research has linked this variant to differences in hormone therapy outcomes for breast cancer patients [3] and susceptibility to estrogen-influenced conditions like migraines [5] and hair loss [2].
Key Insight: The same genetic variant that influences how the body responds to breast cancer hormone therapies also plays a role in female pattern hair loss and migraine susceptibility by modulating estrogen levels.
Location: CYP19A1. Chromosome 15 · 15q21.2 · 51.2 Mb
Estimated prevalence by population
Global 9.2%; European 6.8%; African 9.4%; East Asian 10.1%; South Asian 14.1%; Americas 18.5%; Ashkenazi 5.3%; Finnish 7.9%; Middle Eastern 5.8%; Amish 12.7%.
Estimated AA genotype frequency.
Global 41.3%; European 38.6%; African 42.6%; East Asian 43.4%; South Asian 46.9%; Americas 49.0%; Ashkenazi 35.5%; Finnish 40.3%; Middle Eastern 36.6%; Amish 45.9%.
Estimated AC genotype frequency.
Global 49.5%; European 54.5%; African 48.0%; East Asian 46.5%; South Asian 39.1%; Americas 32.5%; Ashkenazi 59.1%; Finnish 51.8%; Middle Eastern 57.5%; Amish 41.4%.
Estimated CC genotype frequency.
Showing effects for A/A genotype
Organ Systems
Pigmentation & Appearance
Hair Loss. Evidence: 3/10. Source: PMID 19438456. Lower Risk.
Neurology & Mental Health
Headache & Migraine
Migraine. Evidence: 3/10. Source: PMID 22511967. Lower Risk.
Endocrine & Reproductive
Hormone Levels & Endocrine Regulation
Hormone Therapy Response. Evidence: 6/10. Source: PMID 25793413. Variable Response.
Lifestyle, Fitness & Aging
Height & Body Size
Height. Evidence: 7/10. Source: PMID 36224396. Slightly Shorter.
Showing effects for A/C genotype
Hair Loss. Evidence: 3/10. Source: PMID 19438456. Typical Risk.
Hormone Therapy Response. Evidence: 6/10. Source: PMID 25793413. Stronger Response.
Height. Evidence: 7/10. Source: PMID 36224396. Typical.
Showing effects for C/C genotype
Hair Loss. Evidence: 3/10. Source: PMID 19438456. Higher Risk.
Migraine. Evidence: 3/10. Source: PMID 22511967. Typical Risk.
Hormone Therapy Response. Evidence: 6/10. Source: PMID 25793413. Typical Response.
Height. Evidence: 7/10. Source: PMID 36224396. Slightly Taller.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Aromatase activity is generally lower with this genotype, resulting in lower local estrogen levels in tissues like hair follicles and the brain. This reduction in local estrogen levels is associated with a lower risk of developing female pattern hair loss [1]. Additionally, clinical studies suggest that this genotype confers a protective effect against migraines, particularly in women [2]. However, in the context of breast cancer treatment, this genotype is associated with a highly variable response to aromatase inhibitors and tamoxifen [3]. Some studies suggest a poorer prognosis for postmenopausal women on certain therapies, while others show a potential benefit depending on the specific treatment regimen [3].
Lower risk of female pattern hair loss; Reduced susceptibility to migraines; Variable response to breast cancer endocrine therapies.
Sample genotype: AC (Heterozygous)
Balanced aromatase activity with this genotype provides a favorable profile for several health outcomes. Clinical research indicates that individuals with this genotype show a significantly better response and improved disease-free survival when undergoing tamoxifen hormone therapy for early breast cancer [1]. Furthermore, the presence of the A allele is associated with a protective effect against migraines, helping to stabilize susceptibility to hormone-triggered headaches [2]. Hair follicle sensitivity and overall hair loss risk remain at typical baseline levels [3]. This combination of traits suggests a highly favorable genetic profile for both general health and potential medical interventions.
Improved response to tamoxifen therapy; Lower susceptibility to migraines; Typical risk of female pattern hair loss.
Sample genotype: CC (Homozygous)
Higher aromatase activity associated with this genotype can lead to elevated local estrogen levels in various tissues. In hair follicles, these elevated estrogen levels are paradoxically associated with a higher risk of developing female pattern hair loss, particularly in younger women [1]. While this genotype represents the typical baseline for migraine susceptibility, it lacks the protective effect against migraines seen in carriers of the A allele [2]. In the context of breast cancer, this genotype is associated with a typical, standard response to endocrine therapies like tamoxifen and aromatase inhibitors [3]. Additionally, large-scale genetic studies have linked this genotype to a slight increase in adult height [4].
Increased risk of female pattern hair loss; Typical baseline susceptibility to migraines; Standard response to breast cancer hormone therapies.
Variants with shared genetic architecture
rs700519 · CYP19A1 Gene · Chr 15 · Hormone Balance
rs727479 · CYP19A1 Gene · Chr 15 · Endometrial Cancer Risk
rs2899472 · CYP19A1 Gene · Chr 15 · Estrogen and Bone Density
Gene-wide association study between the aromatase gene (CYP19A1) and female pattern hair loss.
A saturated map of common genetic variants associated with human height.
Content updated August 2026.
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