Dietary Bioactive Compounds and Their Role in Allergy Prevention: A Comprehensive Review.

Background/Objectives: Allergic diseases are highly prevalent worldwide and represent a significant public health burden. Current therapies mainly alleviate symptoms without addressing underlying immune dysfunction, which has increased interest in nutritional bioactive compounds as preventive or modulatory agents. This review summarizes evidence on omega-3 polyunsaturated fatty acids, vitamin D, curcumin, ginger bioactives, quercetin, and epigallocatechin gallate (EGCG) in allergy prevention and management. Methods: A comprehensive literature search was conducted in PubMed, Scopus, and Web of Science up to July 2025, including preclinical and clinical studies reporting immunological, mechanistic, and clinical outcomes. Results: Omega-3 fatty acids modulate Th2 responses, promote regulatory T cells, and generate specialized pro-resolving mediators, with modest clinical benefits observed in pregnancy and early life. Vitamin D contributes to immune tolerance and epithelial integrity, although supplementation trials remain heterogeneous. Curcumin inhibits NF-κB/MAPK signaling, enhances barrier function, and improves allergic rhinitis and dermatitis despite limited bioavailability. Ginger constituents ([6]-gingerol, [6]-shogaol) modulate Th1/Th2 balance, mast-cell activity, and oxidative stress, with early clinical evidence in rhinitis and asthma. Quercetin stabilizes mast cells, inhibits Lyn/PLCγ pathways, and improves rhinitis symptoms in small randomized trials using bioavailable formulations. EGCG stabilizes mast cells, attenuates FcεRI signaling, and reduces airway inflammation in preclinical models, though clinical data are scarce. Conclusions: Overall, preclinical findings consistently support the immunomodulatory potential of these compounds, while clinical results are promising but heterogeneous. Standardized formulations, long-term trials, and exploration of synergistic effects are required to confirm efficacy and safety, providing future research directions in allergy prevention.