Question

why should we breathe through nose​

Answer 1

breathing through mouth may cause diseases and thus is because ur mouth may contain waste of food

Answer 2

⇒ I will rather not suggest anyone not to breathe through mouth.

⇒ If we are tired like after running playing games etc the body demand increases for oxygen as such our mouth automatically becomes a second conduit for air to pass.

⇒ After sometime without any consious efforts body will switch to nasal breathing.

⇒ If you are breathing through your mouth primarily or after any nasal obstruction the incoming air is often not conditioned as it would have been if passed through nose like temperature ,humidity , filteration etc .