The act of spitting during a run is a nearly universal experience for athletes. This action results from several complex physiological changes that occur when the body shifts into high-intensity exercise. The body produces and expels excess fluid to manage increased airflow, protect the respiratory system from irritants, and maintain proper lubrication. Understanding these mechanics reveals why this response is a normal, and often beneficial, function of the working body.
Airflow Changes and Airway Irritation
When running, the demand for oxygen increases dramatically, necessitating a shift in breathing patterns. Most runners transition from nasal breathing to mouth breathing, especially at higher intensities, to draw in the required volume of air. This rapid influx of air through the mouth bypasses the nose’s natural filtering and humidifying system, significantly drying the oral and pharyngeal tissues.
The body interprets the sudden drying of the mouth and throat as an irritant. In response, salivary glands are stimulated to produce more fluid to re-moisten and protect the exposed surfaces. This saliva is often thicker than normal because the sympathetic nervous system, activated during exercise, increases the concentration of proteins, such as mucins. Constant air movement across the open mouth causes the water content of this new saliva to evaporate quickly, leaving behind a sticky, concentrated substance that runners feel compelled to expel.
The Respiratory System’s Defense Mechanism
The fluid expelled often includes mucus or phlegm originating from the lower respiratory tract, not just thickened saliva. Running increases the volume of air inhaled, exposing the lungs to more airborne particles, pollutants, and irritants. The bronchial system responds by ramping up mucus production, which acts as a sticky trap for these foreign substances.
This mucus is moved out of the airways by the mucociliary escalator, a coordinated defense system. Tiny, hair-like structures called cilia line the respiratory tract and constantly beat upward, propelling the mucus and trapped debris toward the throat. Once this foreign-laden mucus reaches the pharynx, the body must clear it to maintain open airways, resulting in the need to spit out the accumulated secretions.
Environmental and Hydration Factors
External conditions significantly intensify the body’s need to produce excess fluid during a run. Cold, dry air, common in winter running, is particularly irritating to the nasal and bronchial linings. The respiratory system must work harder to warm and humidify this air, which triggers a greater defensive output of mucus.
Exposure to high levels of pollution, dust, or pollen also forces the respiratory system to produce more mucus to trap and neutralize these irritants. Internally, hydration status plays a large role in the consistency of secretions. If a runner is mildly dehydrated, the body conserves water, making saliva and mucus thicker and stickier than usual. This more viscous fluid is harder to swallow and becomes more noticeable, increasing the urge to spit.
Practical Strategies for Runners
Runners can adopt several practices to minimize the buildup of uncomfortable secretions. Prioritizing pre-run hydration is the most direct way to ensure that any saliva or mucus produced remains watery and easier to swallow. Sipping water frequently throughout the run also helps to dilute thickened oral secretions and reduce the dry-mouth sensation.
Focusing on controlling breathing pace and incorporating more nasal breathing during lower-intensity efforts can reduce the drying effect of constant mouth breathing. For those with significant nasal congestion or a persistent runny nose, using a saline rinse or an over-the-counter nasal spray before a run may help clear the upper airways. If excessive mucus is accompanied by wheezing, persistent coughing, or chest tightness, it may indicate an underlying condition like exercise-induced bronchoconstriction, which warrants consultation with a healthcare professional.