Effect of the Multi‐Strain Probiotic <scp>SYN</scp> ‐53 in the Management of Allergic Rhinoconjunctivitis

Dysbiosis is increasingly linked to allergy development. This study evaluates the efficacy of the multi-strain probiotic SYN-53 in the management of allergic rhinoconjunctivitis (ARC). Eighty-four subjects with confirmed grass pollen allergy underwent up to three bi-weekly 3-day intake cycles with SYN-53 or placebo. After each cycle, subjects were exposed to grass pollen in an allergen exposure chamber. ARC symptoms were assessed using the Total Symptom Score (TSS) before and after each use of SYN-53. After one intake cycle, SYN-53 already showed a trend towards greater efficacy over placebo, which became significant after two cycles (ΔTSS_MAX: -3.44 ± 0.42 vs. -1.87 ± 0.37; p = 0.0067), with 38% vs. 24% symptom relief. In subjects with moderate to severe symptoms, SYN-53 was already significantly superior after one single intake cycle and improved further after two cycles (ΔTSS_MAX: -4.78 ± 0.51 vs. -2.43 ± 0.47; p = 0.0014), with 45% vs. 26% symptom relief. SYN-53 is effective in the management of ARC, highlighting the role of bacterial diversity and dosage in probiotic nutritional supplements.