Stop: You're doing breathwork wrong...

You’ve probably heard the advice countless times —

“Breathe in through your nose and out through your mouth.”

It’s a common cue in yoga, fitness classes, and even stress-management apps. The idea sounds soothing and intuitive — inhale calm, exhale tension.

But here’s the truth: breathing out through your mouth may actually undermine many of the benefits that nasal breathing is designed to provide.

Let’s explore why — from the perspective of physiology, performance, and long-term respiratory health.

1. The Nose Is for Breathing. The Mouth Is for Eating.

It’s a simple principle, but it carries profound implications.
The nasal cavity is not just an entryway for air — it’s a complex filtration, humidification, and regulation system.

When you breathe through your nose, several things happen that don’t happen with mouth breathing:

• Air is filtered through tiny hairs (cilia) and mucus, trapping dust, allergens, and pathogens.

• Air is humidified and warmed, protecting the airways and lungs from dryness and irritation.

• Nitric oxide (NO) — a powerful signaling molecule — is released in the nasal passages, helping dilate blood vessels and improve oxygen delivery throughout the body.

When you breathe out through your mouth, you bypass these benefits and can even reverse them.

2. Mouth Exhalation Can Encourage Over-Breathing

The Oxygen Advantage framework highlights a key idea:

It’s not just how you inhale that matters, but how you exhale.

Exhaling through the mouth tends to increase breathing volume and reduce CO₂ levels more rapidly than nasal exhalation.

That’s a problem — because carbon dioxide (CO₂) isn’t just a “waste gas.” It’s essential for:

• Maintaining proper blood pH balance,

• Regulating breathing rate, and

• Enabling oxygen release to cells (via the Bohr effect).

When you exhale too much CO₂ through the mouth, you can trigger mild hyperventilation, even if your breathing feels relaxed.

Over time, this can lead to:

• Reduced CO₂ tolerance

• Air hunger

• Fatigue or brain fog

• Increased anxiety and heart rate

In contrast, nasal exhalation slows the breath, maintains healthy CO₂ levels, and keeps the nervous system balanced.

3. Nasal Breathing Supports a Calmer Nervous System

Your breathing pattern directly affects your autonomic nervous system — the balance between the sympathetic (“fight or flight”) and parasympathetic (“rest and digest”) branches.

Mouth breathing, especially during exhalation, tends to activate the sympathetic system, subtly signaling stress or alertness.

Nasal breathing, on the other hand, promotes parasympathetic activation, encouraging relaxation, recovery, and mental clarity.

By breathing in and out through the nose, you create a continuous, calm breathing loop — one that supports emotional regulation, focus, and sleep quality.

4. Mouth Exhalation Can Dry Out Airways and Increase Infection Risk

Exhaling through the mouth increases water loss and drying of the respiratory tract, which can lead to:

• Sore throat or coughing

• Dehydration of the mucosal lining

• Greater susceptibility to upper respiratory infections

Your nose humidifies and conditions air both ways — on the inhale and the exhale. Keeping the breath nasal preserves airway moisture, protects against pathogens, and helps maintain respiratory resilience.

5. Athletic Performance and Recovery Suffer

If you train or compete in sports, nasal breathing gives you a performance edge.
It increases CO₂ tolerance, improves oxygen uptake, and reduces breathing rate — all of which lead to better endurance and recovery.

Mouth exhalation, however, can spike respiratory rate, drive off too much CO₂, and increase perceived effort.

In fact, nasal breathing during both inhale and exhale has been shown to:

• Improve oxygen efficiency

• Delay fatigue

• Enhance focus under pressure

It’s one of the cornerstones of the Oxygen Advantage method for athletes.

The Right Way to Think About Breathing

If you take away one message, let it be this:

Keep the breath light, slow, and nasal — both in and out.

A fully nasal breath cycle:

• Filters and humidifies air

• Promotes nitric oxide production

• Balances CO₂ and O₂ levels

• Activates calm, focused states

Of course, there are moments where exhaling through the mouth can serve a purpose — like quick recovery after intense exercise, or deliberate sighing during emotional release. But for everyday breathing, nasal in, nasal out is the smarter, more efficient default.

The Bottom Line

“Breathe in through your nose and out through your mouth” may sound harmless — even soothing — but it subtly trains your body to over-breathe, lose valuable CO₂, and disrupt your natural breathing rhythm.

For better focus, sleep, and energy, keep your mouth closed and let your nose do the work — it’s what it was designed for.

As Patrick McKeown, author of The Oxygen Advantage, often says:

“Close your mouth, and breathe through your nose — all the time, even during sleep.”

Your body, your brain, and your nervous system will thank you.