Runny nose may be caused by cold, allergic rhinitis, upper respiratory tract infection, cerebrospinal fluid leakage and so on. 1. Exposure to cold: When the patient is underdressed, in a cold environment, or exposed to cold wind, it may cause running nose. 2. Allergic rhinitis: allergic rhinitis is a kind of chronic reactive inflammation of the nasal mucosa, the cause of which may be caused by a combination of genetic and environmental factors. Patients may have symptoms such as itchy nose, paroxysmal continuous sneezing, a large amount of watery nasal mucus, nasal congestion and so on. 3. Acute rhinitis: it is acute inflammation of nasal mucosa caused by viral infection, early nasal itching, irritation, foreign body sensation, burning sensation in nasal cavity and nasopharynx, self-consciousness of dryness of nasal cavity, running watery nasal mucus. 4. Cerebrospinal fluid nasal leakage: Especially spontaneous cerebrospinal fluid nasal leakage, most of the time after the head is lowered, the nasal cavity flows clear water. Patients with running water like nasal discharge, it is recommended that patients seek medical examination in time to clarify the cause of the disease for targeted treatment.