There is no fastest treatment for five-month-old babies with runny noses. Runny noses can be caused by colds, rhinitis and other diseases, which can be treated with medication and general treatment. 1. Colds: If the runny nose is caused by colds, it can be sprayed with sea saline under the guidance of a doctor, and if there is more secretion in the nasal cavity, it can be replaced by negative pressure nasal suction under the guidance of a doctor. If necessary, you can follow the doctor’s instructions to apply pediatric cold granules, etc., in order to improve the symptoms. 2. Rhinitis: If the 5-month-old baby’s runny nose is caused by rhinitis, you can use saline to clean the nasal cavity under the guidance of the doctor, and suction care can also help to reduce secretions. If it is allergic rhinitis, attention should be paid to keep the child away from allergens. Normally, you need to observe your baby’s physical condition more often, if your baby has a runny nose, you need to consult a doctor in time.