Shut Your Mouth
The science behind breathing through your nose, and why it might be your easiest health optimizer.
I never gave breathing through my nose that much thought. It’s breathing. It happens. There are other things to optimize.
Then someone close to me started working with a therapist specifically to retrain his breathing: the simple act of breathing through his nose instead of his mouth.
Around the same time, I was planning my return to running after a knee injury, and Instagram served me an ad for a nasal-breathing program for runners. (Say what you will about the algorithm, it’s annoyingly on point.)
And when things converge, I pay attention.
So I went down the rabbit hole. And came back up with science…like compelling science…for something that is truly one of the few longevity protocols that is completely free. Of course, you can work with a practitioner if you want to go deeper (I know a gal if you need), but the basics cost nothing. I’ll give you the punchline up front: close your mouth. If that sounds too simple to make an impact on every system in your body, the research suggests otherwise.
Let’s go.
Why This Boring, Involuntary Action Topic?
Well…because it is actually of the utmost importance. If you’re reading this Substack, you’re either a very supportive friend or someone who thinks about longevity in terms of supplements, biomarkers, training protocols, and mitochondrial health (maybe both!). And yet one of the most well-documented drivers of cardiovascular disease, cognitive decline, and accelerated aging is something that happens while you’re unconscious.
Sleep apnea (to be described below) affects an estimated 54 million adults in the U.S. alone, and the majority are undiagnosed. The reason I’m writing about breathing in a longevity post is that it sits underneath everything else. You can optimize your supplement stack, dial in your nutrition, and train your heart out, but if your airway is collapsing 30 times an hour while you sleep, your body is spending the night in a cycle of oxygen deprivation and stress response that undermines all of it. Breathing is your foundation’s foundation.
Most of us assume we breathe correctly. It’s automatic, of course we do. But estimates suggest somewhere between 17% and 50% of adults are habitual mouth breathers, and many have no idea.
Mouth breathing isn’t just less optimal; it actively works against you.
When you breathe through your mouth, you bypass the nose’s filtration and humidification system, reduce your oxygen uptake efficiency, push your nervous system toward sympathetic dominance (that’s the stress response), and disrupt sleep architecture. Over years and decades, the effects compound in ways that are increasingly well-documented.
A 2025 study found that chronic mouth breathing significantly alters facial bone structure, producing longer faces, receding jawlines, and dental misalignment. And it goes deeper than beauty: the structural shifts also narrows airways, creating a self-reinforcing loop. The breathing problem reshapes the face, and the reshaped face makes the breathing problem worse.
The most vivid illustration of what mouth breathing does to an otherwise healthy person comes from science journalist James Nestor’s work at Stanford, where researchers plugged volunteers’ noses for ten days, forcing them to breathe exclusively through their mouths. The results were immediate and alarming: sleep apnea appeared in people who’d never had it, snoring spiked dramatically, stress hormones rose measurably, and athletic performance declined.
The Dreaded Sleep Apnea Explained
Sleep apnea is when your airway repeatedly collapses during sleep, cutting off oxygen to your brain and body. Each time, your blood oxygen drops, your heart rate spikes, and your nervous system fires a stress response to force you awake enough to start breathing again. Most people don’t fully wake up, so they have no idea it’s happening. But the damage accumulates.
A 2025 meta-analysis found that people with obstructive sleep apnea have an 82% higher risk of cardiovascular events, with severe cases reaching a threefold increase in all-cause mortality. Untreated sleep apnea increases the risk of heart failure by 140% and stroke by 60%. And what’s driving most of that risk is reduced blood oxygen levels from airway obstruction…exactly the thing that nasal breathing is designed to prevent.
The great thing about intervening is that this is reversible. In that same Stanford study, when nasal breathing was restored, nearly all of the alarming results reversed within days. That’s how quickly the body responds to something as simple as the correct route of breathing.
Nitric Oxide: Your Nose’s Hidden Superpower
Nitric oxide (NO) is a vasodilator, meaning it relaxes blood vessels, improves blood flow, and helps oxygen get from your lungs into your cells. It’s also antimicrobial and antiviral. And your nose just...makes it for free in every breath.
Your sinuses produce nitric oxide continuously, and every breath you take through your nose carries it into your lungs. Mouth breathing bypasses this entirely; the nitric oxide stays in your sinuses, unused.
Would you like an 18% improved uptake of oxygen in your blood? Nasal breathing. And as documented in Anatomical Record (2008), “nasally derived NO has been shown to increase arterial oxygen tension and reduce pulmonary vascular resistance,” which means your blood carries more oxygen and your lungs have less resistance to push against. It’s nothing short of a miracle.
In plain English: Your nose produces a molecule that opens blood vessels, fights pathogens, and helps oxygen move from your lungs into your cells. Your mouth doesn’t do any of that. Every breath through your mouth is a missed dose of something your body was designed to receive.
Your Nervous System Is Listening
Nasal breathing activates the parasympathetic nervous system (rest-and-digest). Mouth breathing keeps you in sympathetic mode (fight-or-flight). A 2024 study found that nasal breathing lowered diastolic blood pressure and shifted nervous system state toward parasympathetic, compared directly to mouth breathing in the same subjects.
This is why box breathing (which I mentioned in the recovery post as a way to downshift the nervous system) specifically requires breathing through the nose. The 4-4-4-4 pattern works partly because of the breathing rhythm and partly because of the route.
In plain English: Nasal breathing tells your nervous system “you’re safe.” Mouth breathing tells it “something is wrong.”
Sleep
If you wake up with a dry mouth, snore, or feel unrested even after seven or eight hours, your breathing route during sleep is worth investigating before you buy another sleep supplement.
A 2022 PubMed study on mouth taping in mild sleep apnea patients found that simple oral closure during sleep reduced the apnea-hypopnea index by 47% and the snoring index by 47%. The only variable was whether their mouths were open or closed.
Nestor’s Stanford experiment a few paragraphs back showed the same thing in reverse: healthy people developed sleep apnea and heavy snoring the moment nasal breathing was blocked, and all of it disappeared when they went back to breathing through their noses.
Running and Exercise Performance
This is where things get personally relevant, because I’m rebuilding my running base after a knee injury, and why not maximize while I’m at it? It’s not the first time I’ve heard “breathe through your nose” in the context of running, but…have you ever tried it? It’s hard, and I bet all my runners out there would agree with me. It is just so much easier to breathe through your mouth…why is that? The actual answer is: yes, initially, it feels like fighting for oxygen, even if you know theoretically, logically that it is providing more. That contradiction puzzled me.
The solution is to give it time. A 2025 study confirmed what we all feel: that untrained nasal breathers show a drop in peak performance during maximal effort. But (the bright side) trained nasal breathers show no performance loss at all.
The Dallam study on recreational runners found that after six or more months of nasal breathing training, runners maintained the same VO2 max and peak performance as mouth breathers, but with 22% greater breathing efficiency and lower oxygen cost per breath. And per a Nike running guide on breathing, nasal-trained runners had significantly slower breathing rates (39.2 versus 49.4 breaths per minute) while still delivering more oxygen to muscle cells, specifically because of the nitric oxide effect.
The adaptation window is about six to eight weeks, and it will feel harder before it feels easier; that’s just the training stimulus, the same as any new physical skill.
In plain English: Nasal breathing while running feels difficult at first only because you haven’t trained it. After six to eight weeks, you get the same performance with less effort and better oxygen delivery.
I’m planning to test this myself as I return to running; I’ll report back.
How to Implement This Skill You Didn’t Know You Needed to Fix
During the Day
The simplest instruction: close your mouth. Breathe through your nose.
Start by noticing when you default to mouth breathing. For most people, it’s while concentrating hard, staring at a screen, or feeling stressed. Those are exactly the moments where the parasympathetic shift from nasal breathing would help most.
If you’re congested and feel like nasal breathing isn’t possible, try the Oxygen Advantage approach: exhale gently, hold your breath, walk around until you feel moderate “air hunger,” then breathe slowly through your nose. Most people find this clears the nasal passages within a few minutes. The congestion is often partly functional (not structural) and responds to use.
During Sleep
Mouth taping is the most discussed intervention for nighttime nasal breathing. The idea sounds strange until you think about it; you’re not sealing your mouth shut, you’re just placing a small piece of hypoallergenic tape (3M Micropore works, or purpose-built products like Myotape) vertically over the center of your lips, enough to remind your lips to stay closed without creating a full seal.
The research on this is surprisingly solid. (See the 47% apnea reduction study cited above.)
Important caveat: don’t tape if you have untreated sleep apnea, chronic nasal obstruction, or any difficulty breathing through your nose while awake. The tape works for people who can breathe nasally, but default to mouth breathing during sleep. It’s not a workaround for a structural problem…that is when you’d want to tap a specialist for expertise.
During Exercise
My plan as I rebuild post-injury: start at a slower pace, breathe nose only. When air hunger gets strong enough that form breaks down, exhale through the mouth but keep inhaling through the nose. Gradually extend the distance and pace at which I can maintain full nasal breathing. Expect the first six to eight weeks to feel slower and more labored than usual. Yes, THAT IS A LONG TIME. And at genuine high intensity, mouth breathing is going to have to do, I’m considering mouth breathing as an overflow valve rather than the default route.
Box Breathing
Four seconds in through the nose, four seconds hold, four seconds out through the nose, four seconds hold. I mentioned this in the recovery post as a parasympathetic downshift tool. Now you know why the nasal route specifically matters; the nitric oxide production, the parasympathetic activation, and the slower breathing rate all require the nose to be the entry point.
In Case You Skimmed
Anywhere from 17–50% of adults are chronic mouth breathers, most without realizing it
The sinuses produce nitric oxide with every nasal breath; this increases blood oxygen uptake by 18%; this only happens when you breathe through your nose.
A 2025 study found mouth breathing restructures facial bones over time, narrowing airways further
Ten days of forced mouth breathing caused sleep apnea, snoring, elevated stress hormones, and performance decline in healthy volunteers; all reversed within days of returning to nasal breathing
A 2024 study found nasal breathing lowered diastolic blood pressure and shifted the autonomic nervous system toward parasympathetic state
Mouth taping in mild sleep apnea patients reduced apnea frequency and snoring by 47% each
After a 6–8 week adaptation period, trained nasal breathers maintain identical VO2 max and peak performance as mouth breathers, with 22% better breathing efficiency during exercise.
Have you been paying attention to how you breathe since paragraph one? Probably, and great! Try one full day of deliberate nasal breathing; mouth closed, nose only, during normal daily activity. That’s the whole assignment. Then tack on more days until it becomes your new second nature, you might be surprised about how you feel by next Monday.
See you then,
Susan
Longevity in the Wild
This week, a mom friend of mine asked me what I do for workouts. I told her I weight train, and she lit up. She said that after her second child, she gained more weight than she’d like to have, and gave a local weight training class a whirl. She “magically” lost the weight, and has been consistently going ever since. She didn’t know why it worked; she just knew that it did. And she said it with this look on her face like she’d found a secret no one told her about.
I loved everything about that conversation. Because she’s right; it does work, and the science behind it is straightforward. Muscle is metabolically expensive tissue. The more of it you carry, the more energy your body burns at rest. But resistance training also does something else: it regulates hormones that tend to go sideways after pregnancy and into midlife: estrogen, cortisol, insulin sensitivity. A study in postpartum women found that consistent exercise significantly reduced cortisol and insulin levels, both of which drive fat storage when they’re chronically elevated. She wasn’t imagining the magic; her body was getting the hormonal signal to let go of the weight.
But, truly, what I loved most is that she didn’t need to know any of that. She just followed what her body was telling her, stuck with it, and let the results speak. Not everyone goes down the rabbit hole the way I do, and that’s more than fine. Sometimes trusting what works is its own kind of wisdom.
Wow! Truly didn't know how cool our noses are.