Generally, a one-month-old baby cannot express discomfort, so it is difficult to determine whether they have caught a cold. To judge if a baby has a cold, you need to observe if there are any changes in their usual behavior such as obvious spit-ups, decreased milk intake, increased sleep duration, deeper sleep, inconsolable crying or restlessness, labored breathing, nasal congestion, phlegm sounds in the throat, or frequent bubbles at the corners of the mouth. If the baby's breathing appears faster than usual, it likely indicates sickness. If parents notice their one-month-old is uncomfortable, it is imperative to promptly take the baby to a hospital for a thorough examination and treatment guidance from a specialist doctor.