Updated June 2026
Alternaria Mold Guide (1970)
Alternaria is one of the most common outdoor mold spores and a major late-summer asthma trigger. Real microscope counts, season timing, and relief.
When does Alternaria peak?
Alternaria alternata spores climb through summer and peak in late August and September, often spiking after dry, windy afternoons when crop debris and grass clippings release spores into the air.
Why Alternaria matters
Alternaria sensitization is one of the strongest predictors of life-threatening asthma exacerbations. Even moderate counts can trigger severe symptoms in sensitized children and adults.
Real PollyMap microscope data
The card above shows current Alternaria activity in your area, computed from approved partner microscope samples over the last 7 days.