Breathing, Revisited — Part 3 of 4
This is the third of four pieces in the series Breathing, Revisited. The series returns to breathing from the side of the research, eight years into offering Rolfing sessions. It stands in a different place from the four-part breathing series written back in 2015, during basic training. This third piece takes up how breathing through the mouth changes the shape of the face.
What it means to bring order to the breath
Breath is what I hold to be central in a Rolfing session. Few people are aware of the muscles of breathing — the diaphragm and the intercostals above all — and as a result, a great many carry some trouble in how they breathe.
This piece shares what it means to bring order to breathing through Rolfing, and what goes wrong with breathing through the mouth.
Our ancestors had no need of dentists
In The Story of the Human Body, Daniel Lieberman reports something of interest that emerged while he was looking into the alignment of teeth. Before the industrial revolution, human beings had few cavities and well-aligned teeth, wisdom teeth included; the fossil record makes this clear. After the industrial revolution, alignment begins to go wrong.
At the centre of that book is the idea of mismatch disease — illness arising from the gap between our genes and an environment that has since changed. Dental alignment is treated as one instance of it.
And in Jaws – The Story of a Hidden Epidemic, written by the orthodontist Sandra Kahn and the evolutionist Paul R. Ehrlich, the question of why modern teeth are so poorly aligned is set out with a great many photographs.
The single largest cause they identify is mouth breathing.
Their evidence rests on experiments with rhesus monkeys. The nasal passages of one group were blocked with silicone plugs, forcing mouth breathing, while another group served as controls; followed over time, the first group came to show disordered alignment. Over two years of observation, anterior facial height increased relative to the controls, the angle between the occlusal and mandibular planes widened, and anterior crossbite and tooth malposition appeared.
One thing should be added here. The experiments report considerable variation between animals. And over the two years after the obstruction was removed and nasal breathing resumed, some of the changes reversed. That breathing through the mouth alters the shape of the face is visible as a direction — but it is not a matter of being fixed in one direction for good.
What mouth breathing costs — the effect on dental alignment
What is interesting is that a life centred on mouth breathing gradually narrows the upper jaw. The shape of the mouth deforms into something more tubular, so as to take in more air.
As a result — and it is the tongue resting against the upper palate that lends stability to the posture of the mouth — the space shrinks and the tongue drops. Once the tongue drops, then however much you mean to breathe, the structure of the body narrows the airway. The lower jaw descends along with it, which encourages mouth breathing, and the cycle closes on itself.
In practice, far more people breathe through the mouth than through the nose. In Breath: The New Science of a Lost Art, James Nestor carried out an experiment on himself, plugging his nose with silicone for ten days. Snoring, sleep apnea, lost sleep, and a range of other problems appeared, apparently from the very start of the experiment.
Mouth versus nose — what each does
In The Oxygen Advantage, Patrick McKeown takes up the costs of breathing through the mouth: a tendency toward rounded shoulders, a dry mouth, aggravated snoring. Breathing through the nose, meanwhile, carries a range of benefits, among them an increase in the volume of air taken in.
Daily habits and breathing — what Rolfing can do
Breathing, then, is closely bound up with the habits of daily life. Improve those habits and the quality of breathing changes with them. I take this to yield better results than treating symptom with symptom.
In Rolfing, the work goes to the fascia. Bringing attention to the movement of the diaphragm is how breathing is improved, and it offers an opening for shifting from the mouth to the nose.
Conclusion
This piece has taken up breathing as one of the habits of daily life — how improving it raises the quality of living, and how it bears on a range of modern ailments.
We tend to assume the shape of the jaw was settled at birth. But it shifts according to where the air is drawn from. Fossils take a different shape before and after the industrial revolution. Across that span of time, breathing has been making the shape of the body.
Breathing, Revisited (Four Parts)
- Part 1: A Body That Breathes Too Much — When Carbon Dioxide Runs Short
- Part 2: The Diaphragm Reaches the Heart — Breath, Heart Rate, and Two Nuclei in the Brainstem
- Part 3: The Jaw Is Made by Breathing — Mouth Breathing and the Teeth (this article)
- Part 4: There Are Sensors on the Inside — The Vagus Nerve and Interoception
The breathing series written in 2015, during basic training, is here.
Breathing Series (Four Parts)
- Part 1: Exhaling Takes No Effort — Conscious and Unconscious Breath
- Part 2: The Diaphragm Reaches the Skull — Breath and the Placement of the Organs
- Part 3: When Posture Collapses, Breathing Changes — Extensors, Flexors, and the Scalenes
- Part 4: The Inhaling Body and the Exhaling Body — Breath Seen Through Gravity
Note, September 2026
I wrote this piece in June 2023, and in the body of it I wrote that the tongue resting against the upper palate lends stability to the posture of the mouth, and that when the tongue drops, the airway narrows. That came from the book by Kahn and Ehrlich.
Eleven months before writing it, I had seen the same thing on my own X-ray.
It was July 2022, when I went to Sapporo for treatment on my bite. What the X-ray showed was space within the oral cavity, with the tongue positioned low. The hyoid bone had dropped by the height of one cervical vertebra below where it ought to sit. The airway was narrow as a result, and in that state, breathing would be difficult.
Something else was pointed out to me then. When the load on the internal organs grows too great, the tongue is drawn downward along with it.
What this piece described was one route: mouth breathing narrows the upper jaw, the tongue drops, the airway closes. The order runs from above downward. What I was told in Sapporo ran the other way, from below upward. For the same dropping of the tongue, the road that leads there is not a single one.
There is one more thing this brings to mind. From elementary school into junior high, I had orthodontic treatment. I was told in Sapporo that I carry its effects strongly, and that my bite does not sit where it physiologically should.
This piece opens with fossil teeth taking different shapes before and after the industrial revolution — a matter of thousands, tens of thousands of years. But where my own jaw is concerned, it was a matter of treatment forty years ago and an X-ray eleven months ago. Much closer in.
The jaw is made by breathing. That I could write that came less from reading a book than from having already been shown what was happening inside my own mouth. When I wrote this in 2023, I had not noticed the connection.