It is recommended to use the nose to breathe when breathing normally, and the mouth can be used to assist breathing during strenuous exercise. Normal breathing, breathing through the nose, the nasal cavity contains rich nasal mucosa and nasal hairs, the inhaled air has a filtering effect, blocking the dust and bacteria in the air; breathing through the mouth may lead to dry lips, dry throat, and will inhale a large amount of dust, etc., so in the normal resting state, it is recommended to use the nose to breathe. If during strenuous exercise, in order to inhale more oxygen, you can use your mouth to assist breathing, you can inhale through the nose and exhale through the mouth; or in the case of upper respiratory tract infections with nasal obstruction, you can also use your mouth to assist breathing. In normal resting conditions, it is recommended to use the nose to breathe as much as possible.