In a 9-month-old baby, a cough with mucus (sputum) and a blocked nose are most commonly caused by a viral infection such as the common cold or flu. At this age, babies have narrow nasal passages, so mucus tends to collect in the nose and chest, and they are unable to clear it effectively through coughing. Allergies are less likely but still possible in some cases. You can help by keeping your baby?s nose clear with saline drops, then gently suction with a bulb syringe. Use a cool mist humidifier or keep the air slightly moist. Offer feeds more frequently to prevent dehydration. Keep the baby slightly upright during feeding and when awake, under supervision. Warm baths may also help loosen mucus. Do not use over-the-counter cough medicines, as they are not safe for infants. Seek medical attention if there is fast or difficult breathing, chest indrawing, high fever, poor feeding, bluish lips, or if the baby seems unusually sleepy or irritable. Consult your paediatrician if symptoms worsen or do not improve within a few days.