This paper investigates quercetin for respiratory health with a focus on mechanistic insights and therapeutic potential across viral infections, influenza, COVID-19, allergic rhinitis, asthma, and fibrotic conditions.

Quercetin, a flavonoid widely present in fruits and vegetables, exerts multi-target activities including anti-oxidative defense, anti-inflammatory regulation, antiviral interference, immune modulation, and mast-cell stabilization.

Mechanistically, it scavenges reactive oxygen and nitrogen species, activates the Nrf2–ARE pathway to enhance endogenous antioxidant capacity, suppresses NF-κB and NLRP3 inflammasome signaling to restrain cytokine cascades, and interferes with viral binding and replication through blockade of ACE2–spike interaction and inhibition of viral proteases.

These actions translate into broad clinical relevance.
In acute viral respiratory infections such as influenza and COVID-19, quercetin reduces viral load, strengthens interferon and natural killer cell responses, and alleviates symptom severity and duration.

In allergic airway diseases, including rhinitis and asthma, quercetin mitigates eosinophilic inflammation, modulates Th2 immune responses, and improves airway hyper-responsiveness.

In post-infectious and fibrotic conditions, including pulmonary fibrosis and Post-COVID-19 Syndrome, its combined antioxidant and anti-fibrotic properties contribute to structural protection and tissue repair.

Furthermore, quercetin demonstrates synergistic effects when combined with complementary nutrients such as vitamin C, vitamin D, zinc, bromelain, elderberry, mulberry leaf, and elastin peptides.

Together, these form an integrated “immune stabilization–inflammation resolution–structural repair” framework that enhances both preventive and therapeutic outcomes.

Overall, quercetin emerges as a safe, pleiotropic, and clinically relevant adjunct for comprehensive respiratory health management.