What you carry at this position in your DNA and what research says about it.
Asthma and Allergy Risk: 10/10 evidence, 27 publications.
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Sample genotype (not yours): T/T
Lower Risk of Asthma and Allergies
Two copies of the protective T allele are linked to significantly lower risks of asthma, nasal polyps, and seasonal allergies. This genotype is associated with reduced airway inflammation and lower eosinophil counts.
What this genotype means: Significantly reduced risk of asthma; Lower susceptibility to nasal polyps; Reduced baseline eosinophil counts.
Sample genotype (not yours): C/C
Typical Risk of Asthma and Allergies
Carrying two copies of the common C allele represents the standard genetic baseline for asthma and allergy susceptibility. This genotype is associated with typical levels of airway inflammation and standard eosinophil counts.
What this genotype means: Typical baseline risk of asthma; Standard susceptibility to nasal polyps and allergies; Typical baseline eosinophil counts.
Sample genotype (not yours): T/C
Slightly Lower Risk of Asthma and Allergies
Carrying one copy of the protective T allele offers moderate protection against asthma and allergic conditions. This genotype is linked to slightly reduced airway inflammation compared to the common baseline.
What this genotype means: Moderately reduced risk of asthma; Slightly lower susceptibility to nasal polyps; Slightly lower baseline eosinophil counts.
Gene function and biological role
Gene Function: Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine that plays a critical role in the initiation of allergic inflammation. It is primarily expressed by epithelial cells in the lungs, skin, and gastrointestinal tract. When triggered by environmental factors like allergens or viruses, TSLP activates immune cells to promote type 2 helper T-cell responses. This pathway drives the chronic inflammation characteristic of asthma, eczema, and allergic rhinitis. Consequently, genetic variations that alter TSLP expression levels are major determinants of respiratory health.
Variant Impact: The rs1837253 variant is located in the promoter region upstream of the TSLP gene on chromosome 5. This single nucleotide polymorphism influences the binding affinity of transcription factors, thereby regulating TSLP expression. The protective T allele is associated with lower levels of TSLP secretion from nasal and airway epithelial cells upon stimulation. Reduced cytokine levels lead to less recruitment of inflammatory cells like eosinophils. This molecular shift ultimately lowers the risk of developing asthma, nasal polyps, and other allergic conditions.
Key Insight: A single letter change near the TSLP gene can significantly lower the secretion of inflammatory signals in your airways, acting like a natural shield against asthma and nasal polyps.
Location: TSLP. Chromosome 5 · 5q22.1 · 111.1 Mb
Estimated prevalence by population
Global 8.5%; European 7.0%; African 7.5%; East Asian 38.6%; South Asian 17.9%; Americas 7.3%; Ashkenazi 6.7%; Finnish 5.8%; Middle Eastern 7.8%; Amish 4.3%.
Estimated TT genotype frequency.
Global 39.6%; European 38.9%; African 39.8%; East Asian 47.1%; South Asian 48.8%; Americas 39.5%; Ashkenazi 38.5%; Finnish 36.6%; Middle Eastern 40.2%; Amish 32.9%.
Estimated TC genotype frequency.
Global 51.9%; European 54.1%; African 52.6%; East Asian 14.3%; South Asian 33.3%; Americas 53.2%; Ashkenazi 54.8%; Finnish 57.5%; Middle Eastern 52.0%; Amish 62.8%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Organ Systems
Respiratory Health
Asthma. Evidence: 10/10. Source: PMID 19539984. ~27% Lower Risk.
Nasal Polyps. Evidence: 8/10. Source: PMID 30643255. Lower Risk.
COPD. Evidence: 8/10. Source: PMID 35104449. Lower Risk.
Immunity & Inflammation
Allergy & Hypersensitivity
Allergic Rhinitis. Evidence: 8/10. Source: PMID 21244681. Lower Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Eosinophil Count. Evidence: 8/10. Source: PMID 27863252. Lower Count.
Showing effects for C/C genotype
Asthma. Evidence: 10/10. Source: PMID 19539984. Typical Risk.
Nasal Polyps. Evidence: 8/10. Source: PMID 30643255. Typical Risk.
COPD. Evidence: 8/10. Source: PMID 35104449. Typical Risk.
Allergic Rhinitis. Evidence: 8/10. Source: PMID 21244681. Typical Risk.
Eosinophil Count. Evidence: 8/10. Source: PMID 27863252. Typical Count.
Showing effects for T/C genotype
Asthma. Evidence: 10/10. Source: PMID 19539984. ~16% Lower Risk.
Nasal Polyps. Evidence: 8/10. Source: PMID 30643255. Slightly Lower Risk.
COPD. Evidence: 8/10. Source: PMID 35104449. Slightly Lower Risk.
Allergic Rhinitis. Evidence: 8/10. Source: PMID 21244681. Slightly Lower Risk.
Eosinophil Count. Evidence: 8/10. Source: PMID 27863252. Slightly Lower Count.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Carrying two copies of the T allele provides the strongest genetic protection against several respiratory and allergic conditions. Studies show that this genotype reduces the risk of adult-onset asthma by approximately 27%. It is also associated with a significantly lower likelihood of developing nasal polyps and chronic rhinosinusitis. At the cellular level, individuals with this genotype tend to have lower baseline eosinophil counts, which are key white blood cells involved in allergic reactions. This reduction in inflammatory potential also translates to a lower risk of seasonal allergic rhinitis, commonly known as hay fever. Furthermore, the protective effect extends to chronic obstructive pulmonary disease (COPD), helping preserve long-term lung function. Overall, this genetic profile is highly favorable for respiratory health.
Significantly reduced risk of asthma; Lower susceptibility to nasal polyps; Reduced baseline eosinophil counts.
Sample genotype: CC (Homozygous)
Carrying two copies of the common C allele is the most frequent genetic profile globally and represents the standard baseline for respiratory health. Individuals with this genotype do not carry the protective T allele, meaning they have a typical risk of developing asthma and allergic diseases. This profile is associated with standard levels of TSLP secretion, which can lead to typical inflammatory responses in the airways when exposed to allergens. Consequently, there is a standard susceptibility to conditions like nasal polyps, chronic rhinosinusitis, and seasonal allergic rhinitis. Eosinophil counts and other markers of allergic inflammation are generally at typical baseline levels. There is also a standard risk profile for chronic obstructive pulmonary disease (COPD). While this genotype does not offer the protective benefits of the T allele, it is the normal baseline found in the majority of the population.
Typical baseline risk of asthma; Standard susceptibility to nasal polyps and allergies; Typical baseline eosinophil counts.
Sample genotype: TC (Heterozygous)
Having one copy of the protective T allele and one copy of the common C allele provides a moderate reduction in the risk of respiratory issues. Research indicates that this heterozygous genotype reduces the risk of adult-onset asthma by about 16%. It also offers partial protection against other inflammatory airway conditions, such as nasal polyps and chronic rhinosinusitis. Individuals with this profile typically exhibit slightly lower eosinophil counts than those with the common CC genotype, reflecting a milder allergic response pattern. The presence of the T allele also helps lower the susceptibility to seasonal allergic rhinitis and hay fever. Additionally, studies suggest a modest protective effect against chronic obstructive pulmonary disease (COPD). While not as pronounced as having two protective copies, this genotype still contributes favorably to overall lung and airway health.
Moderately reduced risk of asthma; Slightly lower susceptibility to nasal polyps; Slightly lower baseline eosinophil counts.
Variants with shared genetic architecture
rs3806933 · TSLP Gene · Chr 5 · Asthma and Allergy Risk
rs11071559 · RORA Gene · Chr 15 · Asthma Risk
rs20541 · IL13 Gene · Chr 5 · Asthma and Eczema Risk
Content updated August 2026.
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