So should you use your mouth and nose to breathe in and out or breathe in through your nose and out through your mouth?
Here is what I had to say. I hope it helps!
How you breathe depends on the activity you are doing. The most common instruction for most people is that you should breathe in through the nose and out through the mouth.
Why is this? Is it more efficient or healthier?
Breathing in through the nose and out through the mouth isn’t necessarily more efficient at collecting or transferring oxygen, or expelling carbon dioxide, since those actions take place in the lungs.
However, breathing in through the nose warms, cleans and moistens the air making it less harsh to your lungs, especially on very cold days, and healthier in terms of any initial foreign body or toxin removal.
The hairs in the nasal passages help to filter out foreign bodies and toxins, so cleans the air before it enters the lungs. The nasal passages also contain more mucous which moistens the air, making it easier for transferral into the bronchioles.
Breathing in through the mouth doesn’t have these same benefits, but is still good in terms of how much oxygen you actually take in, and in times of excessive need, such as when short of breath through over-exertion or medical condition, can result in a higher oxygen intake.
Also, in sports applications, for example, it may be wiser to breathe in and out via the mouth. i.e. in boxing if you are punched in the nose while forcefully inhaling or exhaling through the nose you may rupture an ear drum since an exhalation, for example, will be forced into your Eustachian tubes and into your ear. However, an opposing problem with this, using this sport as an example, is that it tends to open the jaw hinge and should you be struck on the jaw, teeth may fracture upon closing or the jaw may break since it is less stable when the mouth is open. This is often why mouth guards are used, so that competitors can mouth breathe to increase they more immediate oxygen intake, to match their increase in adrenalin.
So to summarise, mouth inhalation and exhalation can increase the amount of oxygen you are able to get into your lungs at any one time as opposed to nasal breathing. Nose inhalation particularly better prepares, cleans and warms the air before it enters the lungs.
If you are breathing generally, normally, at rest, or in more relaxed exercise, where the health of the air and lungs is more important, nose breathing is better. If your exercise is slightly more vigorous but not excessively so, inhalation through the nose is better, to maintain that air quality, with exhalation through the mouth, to increase the amount of carbon dioxide you can expel and increase your ability to fully empty the lungs. If your exercise is vigorous or you are short of breath, mouth breathing is generally better to accommodate that shorter time period, and your increased need for as much oxygen as possible. For that short timeframe, oxygen intake overrides attention on the quality of air into the lungs.