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Two and a half billion years ago, Earth was inhabited by some single-cell organisms, but little oxygen.

Then, somewhere around 2.4 billion years ago, some small organisms learned to take energy from the sun and utilize it to create sugar out of water and carbon dioxide.

This process – now called photosynthesis – pumped an enormous amount of oxygen into the atmosphere for the first time, giving rise to cells that could use that oxygen in a symbiotic balance. 

And here we are, all those years later, with ample oxygen around us at all times and we take it for granted.

I believe the fountain of youth lies no further away than the tip of our own nose. If we want to look and feel our very best, it’s as easy as closing our mouth and breathing through our nose. 

In the 1960s, a dentist named Egil Harvold used silicone to plug up the nasal passages of monkeys, forcing them to breathe solely through their mouths.

In a matter of months, their jaws went from a “u” shape to more of a “v.” Their round faces elongated, their teeth grew crooked, and their chins recessed. 

Humans fare even worse under these “plugged nose” conditions, since we are the only animal on Earth that develops more teeth than its jaw can effectively house.

Our elongated faces and narrow jaws cause many of us to breathe through our mouths already. Over time, this causes our chins to recess and our jaws to lower, leaving us in a permanent slack-jaw position. And mouth breathing becomes our default.

We all know mouth breathing is bad for us. Remember those cells that evolved to eat oxygen? We have trillions of them in our body.

Since oxygen is our main source of energy, and exhaling is the main way to get toxins out of our bodies, breathing through the mouth instead of the nostrils means less oxygen in the body. This leads to crooked teeth, bad breath, facial deformities, ADHD, sleep apnea, asthma, recurrent throat infections, hypertension and cancer.

Over time, mouth breathers tend to assume a characteristic “slump” posture, carrying their heads forward and down a little to compensate for the restriction to their airways. 

I believe a large percentage of people who refuse to wear a mask in public do so because they are mouth breathers. This makes wearing a mask much harder – and hotter – than when using proper nasal breathing.

Breathing through your mouth is as efficient as trying to eat through your nose. 

We breathe about 25,000 times a day; it happens automatically, and is something we all know how to do.

So it seems foolish to think that we can (or should) be told how to breathe. Yet, you’ve probably been told to take a deep breath a million times, and maybe you’ve noticed that actually taking the time to take a deep breath helps you feel calmer.

Intuitively, you understand that the breath is the brain’s remote control. Yet most of us aren’t breathing well most of the time, though. 

Fortunately, breathing well is pretty straightforward: Breathe through your nose and down into your belly.

We are designed to breathe through our nose. Nasal breathing moistens and purifies the air as it enters our body; the tiny hairs in the nose called cilia remove three-quarters of the germs in the air.

It is estimated that cilia filters more than 20 billion particles of foreign matter every day.

Inhales and exhales act like a bellow, forcing air into the back of the throat to tone the tissues there. This keeps our airways wider and places less load on our heart to get oxygen to all the cells that require it. 

When we breathe through our nose, we create a neurotransmitter called nitric oxide that dilates the blood vessels in the body to move more oxygen to the brain.

Breathing nasally leads to a 10 percent to 15 percent increase in blood oxidation.

Nasal breathing is a slower process than mouth breathing, so the lungs also have more time to extract oxygen from the air we’ve already inhaled. 

Nasal breathing also engages the diaphragm more than when we breathe through the mouth. Since the diaphragm is under the ribs, it makes sense it would engage the lower lungs more. That’s why our bellies slightly expand like a balloon when we inhale.

The lower lungs are rich in parasympathetic receptors, which engage the “rest and digest” part of our nervous system and leave us with a calm and focused body.

Chest and mouth breathing often triggers the fight-or-flight response, because the breath stays too far up in the chest, where the rib cage prevents full expansion.

When we breathe through our mouths, most adults inhale about a pint of air. But when we take a deep nasal breath, many of us can inhale up to a gallon of air.

Do you snore or suffer from sleep apnea? Google the sleep tape method to retrain your body to default to nasal breathing.

For the rest of us, simply becoming more conscious of our breathing helps to retrain our nose to do its miraculous job. 

Erin Smith is the owner of the OM place in Winchester, the author of “Sensible Wellness” and the online host of the OM channel.