9 months baby has been running nose may be influenza, allergic rhinitis, nasal polyps, as well as chronic sinusitis and other causes. 1. Influenza: Influenza may be caused by pathogen infection such as A virus and B virus. Patients will not only have a runny nose, but also sore throat, high fever, limb pain, fatigue, headache and other symptoms. If the 9-month-old baby has influenza, he may have the symptom of running nose all the time. 2. Allergic rhinitis: Allergic rhinitis is considered to be caused by genetic and environmental factors. Patients will have symptoms such as runny nose, nasal congestion, itchy nose and sneezing. Therefore, a 9-month-old baby with allergic rhinitis will show a runny nose all the time. 3. Nasal polyps: the etiology of nasal polyps is not clear, and it is considered to be caused with the infection of pathogens such as bacteria and viruses, or heredity and metamorphosis. Patients will have symptoms such as nasal congestion, increased nasal secretion, and olfactory impairment. If the 9-month-old baby presents with nasal polyps, it may manifest as a runny nose all the time. 4. Other: 9 months lesion has been running nose is also considered to be caused by chronic sinusitis and so on. 9 months baby has been running nose, there may be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause, under the guidance of the doctor to give targeted treatment or treatment.