The reason for runny nose when it is cold may be caused by physiological factors or pathological factors such as cold, seasonal allergic rhinitis, chronic rhinitis, etc. 1. Physiological factors: pediatric vascular mucosa is rich, more secretions, due to the nervous system has not yet been perfected may appear the phenomenon of runny nose; nasal mucosa stimulated by cold air or drugs, the secretion of the glands in the nasal cavity increased, there will be a phenomenon of runny nose. When it is cold, the eyes will be irritated, and there will be tears in the eyes. There is a thin tube between the eyes and the nose, and the nasal mucous will flow out involuntarily when there is a large amount of tears in the eyes. 2. Pathological factors: cold weather due to cold or infection caused by cold, will lead to runny nose phenomenon, at the same time can be accompanied by dry throat, itchy throat, sore throat, etc.; suffering from seasonal allergic rhinitis, chronic rhinitis patients, can also be stimulated by the cold air when the phenomenon of runny nose. Cold day runny nose, may also be vasomotor rhinitis, etc., can actively seek medical attention to clarify the cause of the disease.