The normal breathing pathway for humans is through the nasal cavity rather than through the oral cavity. In some physiological situations, people will partially use their mouth to breathe, such as during exercise when more air is needed, and nasal breathing will convert to mouth breathing. If, at normal times, breathing through the mouth is abnormal, you need to pay attention! Why does mouth breathing occur? Obstructive diseases of the upper nasal airway are its main cause. Chronic rhinitis, tonsillitis, sinusitis, turbinate hypertrophy, value-added gland hypertrophy and nasal tumor can lead to obstruction or partial obstruction of the upper nasal airway. Once the nasal airway is obstructed, the patient is forced to breathe air through the mouth. Diagnosing mouth breathing is simple, parents only need to put a thin cotton thread in front of the child’s nostrils with little to no airflow in and out of the nasal cavity to blow it around to initially determine if the child has mouth breathing.