Nasal Mucus Composition and Protective Functions

Nasal mucus (snot) is a viscoelastic gel secreted by goblet cells and submucosal glands of the respiratory epithelium. It is the first line of airway defence.

Composition

• Water (95%): Hydration medium.
• Mucins (MUC5AC, MUC5B): Heavily glycosylated proteins forming the gel matrix; trap particles.
• Immunoglobulins: Secretory IgA (primary), IgG — pathogen neutralization.
• Antimicrobial peptides: Lysozyme, lactoferrin, defensins, cathelicidins.
• Enzymes: Amylase, proteases (mucus breakdown).
• Antioxidants: Glutathione, uric acid, ascorbate — neutralize oxidative stress.
• Electrolytes: Na⁺, K⁺, Cl⁻, HCO₃⁻ — osmotic balance, pH buffering.
• Surfactants: Phospholipids — reduce surface tension.
• Cellular debris: Shed epithelial cells, neutrophils.

Functions

• Physical barrier: Traps inhaled particles, allergens, microbes (>5 µm).
• Mucociliary clearance: Coordinated ciliary beating transports mucus blanket to nasopharynx for swallowing (~1 L/day).
• Immune defence: sIgA blocks adhesion; antimicrobial peptides kill microbes.
• Conditioning inspired air: Warms to 37°C, humidifies to 100% RH.
• Olfaction: Dissolves odorants for receptor access.

Pathological Changes

• Viral URI: ↑ volume, ↓ viscosity (watery) → rhinorrhoea.
• Bacterial sinusitis: ↑ neutrophils → purulent (yellow-green).
• Allergic rhinitis: ↑ eosinophils, clear watery, ↑ MUC5AC.
• Cystic fibrosis: Dehydrated, viscous mucus → stasis, infection.
• Primary ciliary dyskinesia: Impaired clearance → chronic sinusitis, bronchiectasis.

Mucus is not waste—it is a dynamic, biologically active interface essential for respiratory health.