Nasal mucus, often called nasal discharge, is a complex, viscous fluid produced continuously by the mucous membranes lining the nose and sinuses. This substance is a sophisticated mixture of approximately 95% water, with the remainder composed of glycoproteins, salts, antibodies, and enzymes. Produced by goblet cells and submucosal glands, this protective blanket maintains the health of the entire respiratory system. Without this constant production, the delicate tissues of the airways would be exposed to environmental threats.
The Nose’s Air Filter: Trapping Dust and Debris
The sticky quality of nasal mucus is a direct result of large protein molecules called mucins, which form a dense, net-like structure. This viscous layer acts as the primary physical barrier, effectively trapping a wide range of airborne contaminants. Particles such as dust, pollen, smoke, chemical pollutants, and even microbes are immediately caught upon contact with this adhesive surface.
Once trapped, the contaminated mucus is continuously moved out of the nasal passages by the mucociliary escalator. Tiny, hair-like projections called cilia beat rhythmically, propelling the mucus layer backward toward the nasopharynx. This transport ensures that particles larger than approximately 3 micrometers are prevented from reaching the lower airways and lungs. The mucus is then swallowed, allowing the stomach’s acid to neutralize any remaining bacteria or viruses.
Conditioning the Air: Temperature and Moisture Regulation
Before air can safely enter the lungs, it must be conditioned to prevent damage to the delicate lung tissues. Nasal mucus, with its high water content, plays a primary role in this process by adding moisture to the inhaled air. The nose is capable of bringing air from 0% relative humidity to a fully saturated 100% before it travels past the throat.
This humidification is important when breathing cold or dry air, as the nasal mucosa must invest significant amounts of water into the airstream to reach the necessary saturation level. Warm blood flowing through the extensive network of blood vessels beneath the nasal lining transfers heat to the mucus. This interaction warms the inhaled air to near body temperature, preventing thermal shock and ensuring the lower respiratory system receives air that is both warm and moist.
Chemical Defense: Immune System Patrol
Beyond its mechanical filtering, nasal mucus contains a potent chemical defense system designed to actively neutralize pathogens. The fluid is rich in specific immune molecules, most notably secretory immunoglobulin A (sIgA) antibodies. These antibodies bind to invading bacteria and viruses, effectively clumping them together to prevent them from attaching to the nasal lining cells.
The mucus also contains powerful antimicrobial enzymes, such as lysozyme and lactoferrin. Lysozyme chemically breaks down the cell walls of certain types of bacteria, dissolving the invaders. When the body detects a significant threat, white blood cells called neutrophils are recruited to the site. The enzymes they secrete can cause the mucus to thicken and change color, signaling the immune system is actively fighting the infection.