The nose not only heats atmospheric air to body temperature by spinning it inside the nasal cavity, but it also moistens the air so that it does not dry out the delicate tissue further down the airway.
The nostrils contain tiny hairs to trap dust, pollen and other airborne particles, and the sticky mucus catches those that the hairs miss. Bacteria are also trapped by mucus and killed by an enzyme found there, or by the concentration of nitric oxide gas that the nose produces.
The mouth, which is the start of the digestive tract, can also be breathed through, but when this happens the body does not receive the same benefits as when the nose is used. Saliva doesn't do the same job as mucus, and there is no spinning of air, warming, moistening or cleaning anywhere near the same degree as found in the nose.
Compared to the mouth, the nasal passages are small, and so less air is likely to be inhaled through the nose, which is useful if you are moving at a reasonable speed or resting, because at these times the breathing should be of a smallish volume.
Yet, while the volume is less, the efficiency of the nose is better. Due to the intricate construction of the nasal passages, air to be driven deeper into the lungs, and as a result, 10% more oxygen reaches the alveoli for gas exchange and transfer into the bloodstream.
It is harder to exhale forcefully through the nose than it is through the mouth, which means that you are less likely to disturb the finely tuned ratio of gases in the lungs if you use your nose to breathe in and out with.
Aromas have been proven to make your mouth water, stimulate an appetite and insulin production, change your mood, reduce depression, and assist with insomnia. The sense of smell provided by the nose gives us a wide range of information about people and our surroundings, as well as bringing joy, disgust, and triggering memories. In short the nose makes you realise that you are alive!
Like many other functions, the nose seems to have a 'use it or lose it' property. And while it will not fall off your face if you habitually breathe through your mouth, it will not work anywhere near as good as it should. So use it regularly: almost every breath you take. To clear a blocked nose try this exercise.
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