Level 1: Causes of baby\’s runny nose 1.1 Cold virus infection The most common cause of baby\’s runny nose is cold virus infection. In this case, the nasal discharge is usually watery or sticky. 1.2 Allergic reaction If your child has a runny nose accompanied by allergy symptoms such as sneezing and itchy eyes, it may be due to the child being allergic to certain substances. 1.3 Dry air Dry air can also cause a runny nose in babies, because the dry air will cause the secretions inside the nasal cavity to change.