xRead - Nonallergic Rhinitis (September 2025)

Clinical Reviews in Allergy & Immunology (2024) 67:40–46

45

Conclusions and Limitations This systematic review and meta-analysis, encompassing eight studies, demonstrate that capsaicin treatment holds potential for alleviating symptoms in patients with non allergic rhinitis (NAR). The observed improvements in total nasal symptom scores (TNSS) and visual analog scale (VAS) scores, coupled with a higher proportion of thera peutic respondersin capsaicin–treated patients, support its efficacy. The mechanism underlying capsaicin’s thera peutic effect is likely attributed to its interaction with the TRPV1 receptor, which effectively modulates the TRPV1 SP nociceptive signaling pathway in the nasal mucosa. However, it is crucial to acknowledge the limitations inherent in this meta-analysis. The findings are based on a relatively small number of studies, characterized by methodological heterogeneity and potential biases, which warrant further investigation. Furthermore, the lack of standardization in outcome rating methods across studies limits the ability to draw definitive conclusions regarding the efficacy of different capsaicin doses. Several studies also suggest alterations in other nasal symptoms and biochemical markers, such as reduced sub stance P levels and decreased TRPV1 expression, high lighting the complexity of capsaicin’s effects on nasal physiology. However, these findings require further explo ration and validation through larger and more rigorously designed studies. To solidify the role of capsaicin in NAR management, future research should prioritize larger scale clinical tri als with standardized methodologies and robust outcome measures. Employing advanced diagnostic techniques to accurately classify NAR subtypes will also improve the validity of future studies. The exploration of capsaicin’s efficacy and safety across a wider patient population, encompassing diverse demographics and clinical presen tations, is crucial for establishing its clinical utility and deepening our understanding of its molecular mechanisms in alleviating nasal symptoms. In conclusion, while this meta-analysis provides encour aging preliminary evidence for the efficacy of capsaicin in treating NAR, further research is needed to establish its definitive role in clinical practice. Author Contribution Jiatong Wang: Methodology, Formal analysis, Investigation, Data Curation, Writing—Original Draft, Writing— Review & Editing, Visualization, Supervision, Project administration Leilani Zhang: Methodology, Validation, Investigation, Data Cura tion Kangyang Zheng: Methodology, Validation, Investigation, Data Curation. Data Availability No datasets were generated or analyzed during the current study.

Fig. 4 Funnel plot of comparison capsaicin versus placebo for NAR in VAS or TNSS at the ends of studies. Vertical axis, standard error of std. mean difference. Horizontal axis, std. mean difference

major symptoms, indicating a possible role of TRPV1 in symptom severity. Substance P levels, elevated in patients with NAR compared to healthy controls, were reduced to control levels after capsaicin treatment [3]. However, in a later study, Van Gerven found no reduction in PGP9.5, TRPV1, TRPV4, TRPM8, and nerve growth factor (NGF) expression in patients with idiopathic rhinitis 4 and 26 weeks after capsaicin treatment using polymerase chain reaction (PCR) tests. Interestingly, baseline human TRPV1 expres sion is correlated with the results of the trigeminal reflex test (TRE) 12 weeks after capsaicin treatment [6]. Van Gerven further reported a positive correlation between substance P concentration and major nasal symptoms, suggesting its potential as a biomarker to predict therapeutic response [7]. While we cannot definitively compare the effectiveness of different doses due to inconsistent outcome measurement methods across studies, we can still draw upon the accumu lated clinical experience to offer practical, albeit tentative, suggestions for dosage. There are four records mentioning the concentration of capsaicin used in studies, all of which utilized a 0.1 mmol/L capsaicin solution. Among them, one study tested both a 0.1-mmol/L and a 0.01-mmol/L solution [1, 6–8]. In Van Gerven’s 2021 study, low doses of capsaicin were considered as eligible as the 0.1-mmol/L solution, but we cannot compare the superiority of the 0.1-mmol/L and 0.01-mmol/L solutions. However, the 0.1-mmol/L solution is more commonly employed in clinical trials [7]. Different Doses of Capsaicin Applied in the Studies