Xerostomia and the endurance athlete

Why Exercise Dries Out Your Mouth - It's not what you think 

If you’ve ever been deep into a long ride or run and felt like your mouth suddenly turned into sandpaper, you’ve experienced what athletes commonly call cottonmouth. In dentistry, we use terms like hyposalivation (reduced saliva flow) or xerostomia (dry mouth), but they all describe the same thing: your mouth stops producing enough saliva when you need it most.

During exercise, this dry mouth isn’t random. It comes from two primary physiological changes: how we breathe and how the nervous system reallocates resources.

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1. Breathing Changes: Nose to Mouth

At rest, most people breathe primarily through their nose. Nasal breathing helps humidify and warm incoming air, which protects oral tissues. But once exercise intensity rises and oxygen demand increases, the body naturally shifts toward mouth breathing to maximize airflow and gas exchange.

That increased airflow across oral tissues accelerates evaporation—drying out the tongue, cheeks, and teeth. It’s the same reason people who sleep with their mouths open often wake up with a dry mouth. During endurance exercise, this effect is amplified by duration and intensity.

2. The Sympathetic Nervous System: Fight or Flight

The second—and more important—factor is activation of the sympathetic nervous system, commonly known as the “fight or flight” response.

You’ve probably heard the contrast:

• Parasympathetic = rest and digest

• Sympathetic = fight or flight

Exercise pushes the body firmly into sympathetic dominance. Blood flow is redirected toward working muscles, the heart, and lungs—where it’s needed most. As a result, blood flow is pulled away from organs that aren’t essential for immediate survival, including:

• Salivary glands

• The stomach and intestines

• Other digestive tissues

A simple way to think about it:
If you’re running from a bear, your body sends blood to whatever helps you escape—not to making saliva.

From a whole-body perspective, this makes sense. Reduced saliva production conserves water and allows the body to prioritize performance. But from an oral health perspective, this tradeoff comes at a cost.

Why Saliva Matters So Much for Teeth

Saliva isn’t just “spit.” It plays several critical protective roles:

1. Buffering Acids

Saliva helps neutralize acids in the mouth and return pH toward neutral. When saliva flow drops, buffering capacity decreases, meaning acids from sports drinks, gels, and bacterial metabolism stay active longer and dissolve enamel more effectively.

2. Remineralization

Saliva is the delivery system for calcium and phosphate, the two key ions required for enamel remineralization. Reduced saliva means fewer minerals reaching the tooth surface at exactly the time they’re needed most.

The result?
Longer acid exposure, slower recovery, and higher risk for:

• Enamel erosion

• Sensitivity

• Cavities

What Athletes Can Do During Training and Racing

You can’t turn off your sympathetic nervous system mid-race—but you can reduce the damage.

Practical, In-Race Strategies

• Drink water frequently, especially during long efforts

• Rinse with water after gels or carb drinks when possible

• Avoid constant sipping of diluted carbohydrate drinks—this extends acid and sugar exposure

• Separate fueling from hydration when feasible

• Use saliva stimulants, such as xylitol gum, post-ride or during lower-intensity segments

Rinsing doesn’t eliminate risk, but it shortens the time enamel is exposed to sugars and acids, which meaningfully reduces cavity risk over time.

From the Chair: Key Clinical Takeaways

• Exercise increases sympathetic nervous system activity, which reduces saliva production

• Reduced saliva means less buffering and less remineralization

• During training and racing:

  • Drink water often

  • Rinse after gels and carb intake

  • Space out fueling when possible

• Saliva stimulants like xylitol gum can help jump-start saliva production once intensity drops

Your fueling strategy may be optimized for performance—but your teeth are experiencing that same strategy very differently. Understanding what’s happening physiologically is the first step toward protecting both.