Every season brings changes in humidity, temperature, and environmental exposure shaping not just our comfort, but the delicate microbial ecosystem in our nasal passages.
1. Seasonal Dynamics of the Nasal Microbiome
Longitudinal sampling of healthy individuals shows that both bacterial and fungal communities in the sinonasal cavity shift with seasonal and annual variations even though each person retains a unique microbial “signature” (Yan et al., 2019). Additionally, nasopharyngeal microbiome diversity fluctuates markedly from autumn to spring (ASM Systems Lab, 2025).
2. Climate Factors Alter Microbial Balance
Climate variables temperature, rainfall, atmospheric pressure, and humidity are strongly correlated with shifts in nasal microbiota composition. For instance, as humidity changes, levels of certain species rise or fall (MicrobiomePost, 2019).
3. Allergies and Air Pollution Disrupt Stability
Individuals with seasonal allergic rhinitis experience notable microbiome alterations when exposed to allergens compared to non-allergic individuals (Biswas et al., 2013).
Moreover, traffic-related air pollution has been shown to increase the richness and alter the composition of the nasal microbial community in healthy adults. In children, winter pollution is associated with reduced nasal microbiome diversity and shifts toward potentially harmful bacterial communities (Thomas, 2025).
4. Indoor Environment & Air Conditioning
Indoor environmental conditions including relative humidity, temperature, and ventilation systems significantly influence airborne microbial exposure, impacting the nasal microbiome (Indoor bioaerosol studies). Air conditioning, while beneficial for comfort, often lowers indoor humidity beyond optimal levels (40–60%), potentially irritating nasal passages and disrupting microbial balance (Time, 2025).
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The nasal microbiome operates like a climate-responsive ecosystem.
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Seasonal changes, allergens, pollution, and indoor air factors can all disrupt its protective balance.
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Maintaining stable, moderate indoor humidity (approx. 40–60%) and minimising pollutant exposure may support better nasal microbial health and enhance local immune defense.