Mold spore guide
Cladosporium Mold Guide
Cladosporium is the most common airborne mold spore outdoors. Learn when it peaks, what it looks like under the microscope, symptoms, and where to find local counts.
Quick answer
Cladosporium is usually the #1 outdoor mold spore in U.S. air samples. It grows on leaves and plant debris and is released in large numbers on dry, windy days.
What Cladosporium looks like
Under the microscope, Cladosporium spores are small, pale to olive-brown, oval to lemon-shaped, and often appear in short branching chains with visible attachment scars.
Season
Spores are present much of the year but rise through late spring, peak in summer and early fall, and drop after hard frost.
Symptoms
Runny nose, sneezing, itchy eyes, cough and asthma flares in sensitized people — often overlapping with grass and weed pollen season.
Reducing exposure
- Keep windows closed on dry, windy afternoons.
- Wear a mask when mowing or raking leaves.
- Fix indoor moisture and keep humidity below 50%.
Frequently asked questions
- Is Cladosporium dangerous?
- For most people it is harmless, but it is a common allergy and asthma trigger for people sensitized to mold.
- When is Cladosporium highest?
- Counts usually peak in summer and early fall, especially on warm, dry, breezy afternoons.
- Can Cladosporium grow indoors?
- Yes. It can grow on damp window frames, bathrooms and HVAC components, though most airborne Cladosporium comes from outdoors.
- How do I find Cladosporium counts near me?
- PollyMap publishes local mold findings from air samples verified in the PollyKit Lab. Check the latest reports or subscribe with your ZIP code.