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Background House Dust Mite (HDM) is the most common indoor allergen triggering allergic symptoms. First‐line pharmacotherapy treatment is recommended in international guidelines, while the avoidance of allergens represents a still unmet guideline principle. AM‐301 is a new non‐pharmacological nasal spray that creates a protective gel‐like barrier on the nasal mucosa, preventing the contact with the allergens. Methods This randomized, open‐label, 3‐period crossover study assessed the efficacy and safety of AM‐301. The objective was to determine whether AM‐301 reduces allergic rhinitis (AR) symptoms in patients exposed to HDM allergens. Adults with confirmed Perennial Allergic Rhinitis (PAR; n = 37) were exposed to HDM allergen in a controlled Allergen Exposure Chamber before and during a treatment course of AM‐301 (in six different sequences) within 3 weeks (A: One spray AM‐301 per nostril/B: Two sprays AM‐301 per nostril/C: no treatment). For the primary efficacy analysis, data from the total nasal symptom score (TNSS) were pooled from treatment A + B (D) and analyzed with Analysis of Covariance Model. As secondary endpoints, single time points, visits and symptoms were analyzed. Results The primary endpoint (overall change in TNSS from baseline over all three visits) showed significant results (p = 0.0085). A comparable alleviation of all four symptoms (itchy nose, nasal congestion, runny nose, sneezing) by the protective layer started to emerge after 40 min and lasted up to 180 min (end of challenge). AM‐301 resulted to be safe and well‐tolerated. Conclusion AM‐301 significantly reduced HDM‐related allergic symptoms in a standardized allergen challenge. Protection was observed to last up to 180 min.