A clear runny nose at night may be caused by vasomotor rhinitis, allergic rhinitis and other reasons. 1. Vasomotor rhinitis: it is mainly caused by the dysfunction of the autonomic nervous system. Environmental factors such as temperature, air pressure, irritating gases can stimulate nasal symptoms. Nasal congestion, runny nose, sneezing, nasal itching are common. Some patients have clear running nose as the main symptom. Temperature changes at night may cause patients to develop vasomotor rhinitis. 2. Allergic rhinitis: patients may be allergic to the mites on the bedding, and when patients lie in bed, contact with allergens induces an allergic reaction, which may cause symptoms such as nasal itching, sneezing, runny nose and nasal congestion. When the patient has the symptom of running nose at night, it is recommended to go to the hospital for examination and diagnosis in time, and choose the appropriate treatment under the guidance of the doctor.