Mold season in St. Louis hits hardest in the late summer and fall, when humidity lingers and fallen leaves pile up. The damp autumn air, combined with warm days and cool nights, creates perfect conditions for mold to thrive. If you have allergies or asthma, you might notice more sneezing, itchy eyes, or congestion. Many locals track mold counts like they do pollen, because the levels can spike dramatically. It's a real challenge here, especially near the rivers and older homes with basements. mold season St. Louis 30