It may be the most natural thing in the world, but breathing is surprisingly easy to get wrong – and that matters more than you might think.

Most of the time, the right way to breathe is through your nose. The nose  is exquisitely designed to trap dust and other foreign bodies.  Beyond your visible nose lies the nasal cavity, a cavernous space the size of a gaping mouth. This is lined with folded membranes designed to warm or cool the air to body temperature, add moisture and trap pathogens in yet more mucus. Your sinuses – air-filled spaces that connect to the nasal cavity – swirl the air around more and add nitric oxide, which kills bacteria and viruses and relaxes the blood vessels in the respiratory tract, allowing more oxygen to pass into the blood.

The upshot of all this is that nose breathing adds 50 per cent more air resistance than breathing through the mouth. That gives your heart and lungs a workout and increases the vacuum in your lungs, which allows you to draw in up to 20 per cent more oxygen than breathing by mouth.

As if that wasn’t enough, nasal breathing boosts brain function and is important for learning and memory.  The explanation is that the nasal cavity has a direct line to the emotional and memory processing centres of the brain, via sensory neurons that connect to the brain’s olfactory bulb.  These neurons sense air moving in and out of the nasal cavity and lock brainwaves to the same rhythm.   Synchronised brainwaves then spread beyond the scent-processing brain areas into regions responsible for memory, emotion and cognition.

Nil by mouth

According to some estimates, more than 50% of children and 61% of adults breathe through their mouths too often. As a result, we also risk bad breath, poor sleep, learning difficulties, tooth decay and even malformation of the jaw.

As for how fast to breathe, if it is calm you seek, slow it down to about six breaths per minute. This triggers a reflex that widens blood vessels and reduces heart rate. Concentrating on a long, slow exhalation also stimulates the vagus nerve, which is in charge of the rest-and-digest response, the opposite of fight or flight. Breathing more slowly still might even lull you into an altered state of consciousness  lAt three breaths per minute, theta brainwaves increase together with a zoned-out state that looks like slow-wave sleep, a deep state of slumber.

There is also humming. Humming sets up swirls of air in the sinuses, which boost production of nitric oxide  15-fold, with all its immune and cardiovascular benefits. The only time that nose breathing falls short is when you need to fill your lungs quickly. In an emergency, a gasp of air through the mouth works wonders. Just try not to make a habit of it.  (Lightly edited version of a recent article by Caroline Williams, in the New Scientist, 8 Jan 2020, On health)