Why is this happening? He usually just takes a quick shower right before bed. But he seems to always have a cough or sniffling nose and sometimes even wakes up sick with cough and runny nose. It happens more often during colder months. He takes showers 2-3 times per week, sometimes more sometimes less. He goes straight from shower, wipe, robe, pajamas and then bed. So he doesn’t get overly cold. Why is this happening? What can I do to change it? Any tips please.

Edit: don’t have mold. Sometimes dry air in winter but we use a humidifier.