Level 1: Causes of baby\’s runny nose There are many reasons for baby\’s runny nose, which may be caused by colds, allergies, climate change and other factors. Colds are the most common cause and are usually accompanied by symptoms such as fever and cough. Allergic rhinitis, which causes symptoms such as sneezing and nasal congestion, is usually caused by allergens such as pollen and dust mites. Climate change can also cause a runny nose in babies. The temperature rises suddenly from winter to spring, and the humidity in the air will also change, which may irritate the baby.