There are several reasons for a baby’s strong nighttime cough with phlegm: 1. Acute bronchitis or pneumonia, as the virus invades the trachea or lung tissue, resulting in congestion, edema, and increased mucus secretions in the bronchial mucosa walls or alveoli, forming phlegm and stimulating the production of a cough, which requires a chest X-ray to confirm the diagnosis. The diagnosis can be confirmed if it shows increased lung texture or scattered punctate shadows in both lungs. 2. Mycoplasma infection, the onset of this particular pathogenic infection is characterized by irritating cough at night, and blood can be drawn for Mycoplasma pneumoniae to clarify the diagnosis, and after the diagnosis is confirmed, it is necessary to clear the mycoplasma by standardizing the course of oral or sedative macrolides. 3. The incidence of allergic cough has increased significantly due to the decline in air quality, especially in winter when haze is severe. If this is the case, you need to take oral anti-allergy medication or nebulized inhalation medication to relieve the condition.