Q&A: My 10-week-old son has congestion in his chest. Does he have a cold or allergies?

I can't tell over the internet whether congestion is due to a cold or allergies, except to tell you that seasonal allergies (ie: hayfever) don't start for at least a few years. If an allergy is present, it is more likely an 'indoor' allergy to dust or mold, neither of which is as common as the common cold.

The rattling sound can fool you. It can either be from the lungs or transmitted from the nose and sound 'chesty'. The fact that your son isn't having trouble breathing is reassuring, but to really get the answer, someone would need to take a good listen. If his symptoms persist, if his rectal temperature rises above 100.4, if he is having trouble breathing or begins to look ill, take him in.