Allergies: could the gut hold the key?

#SeasonalAllergicRhinitis #Probiotics #Prebiotics #GutMicrobiota  


Seasonal allergic rhinitis (SAR) is a chronic inflammatory condition of the upper airways, driven by an inappropriate immune response to environmental allergens such as pollen. It is characterized by classic symptoms — sneezing, runny nose, nasal congestion, and itching — that significantly impair quality of life. Its prevalence is steadily rising, now affecting nearly 40% of the global population, underlining its major public health impact and increasing economic burden.  

Standard treatments mainly include antihistamines, intranasal corticosteroids, and allergen-specific immunotherapy. While often effective, these approaches have limitations: side effects, individual variability in treatment response, low adherence, and frequently only partial long-term efficacy. This reality highlights the need for complementary or alternative therapeutic strategies, especially those targeting the underlying mechanisms of the disease.  

In this context, a new therapeutic avenue has emerged: modulating the gut microbiota, a key player in immune homeostasis. Recent studies have revealed alterations in the microbiota of patients with SAR, suggesting a potential link between intestinal dysbiosis and worsening allergic symptoms.  

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A healthier microbiota, calmer symptoms?  

Conducted on 106 patients aged 18 to 65, the study compared a group receiving daily supplementation with probiotics (including Bifidobacterium longum, Lactobacillus acidophilus, etc.) and prebiotics (fructo-oligosaccharides, inulin...) for 90 days, against a placebo group. Evaluation criteria included the Total Nasal Symptom Score (TNSS), quality-of-life questionnaires, immune markers (TNF-α, INF-γ, IL-17, IgE), as well as analysis of gut microbiota (16S rRNA, qPCR) and its metabolites (short-chain fatty acids – SCFAs).  

By the end of the study, patients who received the supplementation showed a significant improvement in SAR symptoms, particularly reduced TNSS, less rhinorrhea, and fewer sneezes. On an immune level, TNF-α and INF-γ levels increased, while IL-17 decreased, indicating a favorable rebalancing of the immune response. IL-4 and IgE levels remained stable.  

The intervention also altered the gut microbiota. Populations of Lactobacillus, Veillonella, and Bifidobacterium increased, along with production of acetate, a metabolite beneficial for immune health. In addition, several metabolic pathways involved in immune regulation — including those of purines, tyrosine, and glycolysis — were enhanced. These shifts in the microbiota’s composition and function correlated with symptom improvement, suggesting an action mediated by the gut-lung axis.  

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The microbiota on the front line  

Seasonal allergic rhinitis (SAR) is a common inflammatory disorder triggered by pollen exposure, marked by an exaggerated immune response. Despite available treatments, many patients continue to experience debilitating symptoms, and conventional options don’t always provide lasting relief. This study aimed to assess the impact of daily probiotic and prebiotic supplementation on SAR symptoms, while also exploring related changes in the gut microbiota and immune response.  

The intervention reshaped the gut microbiota, promoting the growth of Lactobacillus, Veillonella, and Bifidobacterium, while boosting production of acetate — a short-chain fatty acid with recognized immunomodulatory properties. At the same time, key metabolic pathways involved in immune regulation, particularly purine and tyrosine metabolism, were activated. These changes in microbial composition and function were closely tied to symptom improvement, supporting the hypothesis of a central role for the gut-lung axis in allergic response modulation.  

This study reinforces the idea that the gut microbiota is a promising therapeutic target for relieving seasonal allergic rhinitis. The combination of probiotics and prebiotics proved effective, well tolerated, and free of major side effects, positioning microbiota modulation as an innovative approach to managing allergic conditions. However, some limitations should be considered, underscoring the need for further research. Tailoring interventions based on individual microbial profiles could enhance effectiveness. Larger-scale and longer-term studies will be essential to confirm these findings and better identify the patients most likely to benefit from this treatment.