Quercetin

Quercetin is a plant flavonoid with antioxidant, anti-inflammatory and mast-cell–stabilizing actions that make it biologically plausible as a supportive treatment for chronic rhinosinusitis (chronic sinusitis). However, strong clinical proof for quercetin specifically as a treatment for human chronic rhinosinusitis is limited — most human trials target upper-respiratory infections or allergic rhinitis and many CRS studies are preclinical (animal or cell) or small/uncontrolled human reports.

• Mast-cell stabilizer / antihistamine effect. Quercetin inhibits histamine, leukotrienes and multiple pro-inflammatory cytokines from human mast cells — and in direct comparison it reduced cytokine release more effectively than cromolyn in cell studies. That mechanism is directly relevant to allergic / inflammatory nasal disease. PLOS
• Anti-inflammatory / cytokine down-regulation. Quercetin suppresses NF-κB and decreases IL-1β, IL-6 and other pro-inflammatory mediators in cell and animal models — pathways implicated in chronic rhinosinusitis. SpringerLink BioMed Central
• Antioxidant + epithelial protection. It scavenges reactive oxygen species and has been shown in animal models to reduce epithelial apoptosis and mucosal remodeling in CRS models (improves nasal mucosal histology). SpringerLink Europe PMC
• Potential mucociliary / secretory effects. Some preclinical work suggests quercetin can affect ion channels and ciliary function (mechanisms that matter for sinus drainage), though human data here are limited. SpringerLink

Summary: mechanisms are biologically plausible and fairly well demonstrated in vitro and in animals; human evidence for chronic sinusitis specifically is preliminary. PLOS SpringerLink

Oral dosing (human trials):

• Large community RCTs of upper-respiratory infections used 500 mg or 1,000 mg per day (oral) for 12 weeks. Results were mixed overall; some subgroups saw fewer sick days. Europe PMC Queen's University Belfast
• Small randomized trials for other inflammatory conditions have used ~500 mg/day. University of Alabama at Birmingham

Improved-absorption formulations:

• Because native quercetin is poorly absorbed, many studies and products use phytosome / liposomal / nano-formulations (e.g., Quercetin Phytosome® / Quercefit®). Pharmacokinetic studies show phytosome formulations substantially increase plasma quercetin vs standard preparations. If you choose oral quercetin, a phytosome or liposomal form typically gives higher and more consistent blood levels. SpringerLink Indena

Combination products used in ENT studies:

• An open clinical report of “Quercimmun™” (quercetin phytosome 250 mg + zinc 5 mg) used 2 tablets/day for 60 days reported symptom improvement in chronic allergic and non-allergic rhinitis (non-randomized, uncontrolled). This is the kind of dosing/formulation actually used in recent ENT practice reports. Austin Publishing Group

Topical / intranasal delivery (preclinical / experimental):

• Animal studies and formulation research have tested intranasal quercetin (or quercetin in nanoparticles/liposomes) and reported mucosal anti-inflammatory effects. Intranasal approaches are experimental and mostly in animal models or early formulation work — not standard clinical practice yet. ResearchGate ScienceDirect

Practical pattern often seen in practice/research

• Choose an oral dose consistent with human trials (commonly 500 mg/day or up to 1,000 mg/day) for short courses (studies up to ~12 weeks). Prefer bioavailable formulations (phytosome/liposomal) or co-formulations with absorption enhancers (bromelain, vitamin C, sometimes piperine — note piperine may affect drug metabolism). For chronic nasal symptoms some clinicians use phytosome quercetin + zinc regimens like 250 mg twice daily for 60 days (as in the Quercimmun report). Europe PMC Austin Publishing Group SpringerLink

Human clinical trials (relevant but not definitive for CRS):

• Large RCT (upper respiratory infections): randomized, double-blind, placebo-controlled trial comparing 500 mg and 1,000 mg/day quercetin vs placebo in ~1,000 subjects (12 weeks). Outcome: overall no large reduction in URTI incidence, but some subgroups (e.g., older/physically fit people at the 1,000 mg dose) had fewer sick days. This shows possible benefit for upper-respiratory symptoms but not CRS specifically. Europe PMC Queen's University Belfast
• Small controlled trials in allergic conditions / inflammatory disease: a number of small trials used ~200–500 mg/day or phytosome formulations and reported improvement in allergic rhinitis symptoms or markers of inflammation — several are small or use specialized formulations. (Example: randomized phytosome study in pollinosis reported improvement.) European Review Austin Publishing Group

ENT / sinus-specific studies (preclinical / early clinical):

• Animal & cellular CRS models: multiple recent animal studies show quercetin reduces nasal mucosal inflammation, mast cell infiltration, cytokines (IL-1β, IL-6, IL-4), epithelial apoptosis and polyp formation in CRS models. These are supportive mechanistic data but are not human RCTs. Example: Quercetin Alleviates the Progression of Chronic Rhinosinusitis (Molecular Biotechnology, 2024/2025). SpringerLink ScienceDirect
• Open clinical/retrospective ENT report: Quercimmun™ (quercetin phytosome + zinc) given 250 mg × 2 daily for 60 days in 36 subjects with chronic rhinitis reported symptom improvements (uncontrolled, preliminary). Authors caution results are preliminary and need randomized trials. Austin Publishing Group

Mechanistic and in-vitro evidence (important support):

• Mast cell inhibition vs cromolyn: PLOS ONE study showed quercetin more effectively inhibited histamine, leukotriene and cytokine release from human mast cells than cromolyn — a key mechanistic paper relevant to allergic/inflammatory nasal disease. PLOS

Systematic / review articles:

• Reviews of quercetin’s anti-inflammatory and anti-allergic properties summarize in-vitro, animal and limited clinical evidence and highlight potential but call for more robust human trials. BioMed Central MDPI