Question

why should we breathe in only through our nose ?

Answer 1

The lungs are a primary source of our energy level. They extract oxygen from the air we breathe primarily on the exhale. Because the nostrils are smaller then the mouth, air exhaled through the nose creates back pressure when one exhales. It slows the air escape so the lungs have more time to extract oxygen from them.

Answer 2

Well breathing though the nose is much safer and a much smoother process than breathing through the mouth as the nose contains hair and mucus that help in trapping dust particles and thus preventing them from entering the wind track