Houston Mold Count
Measured counts from the Houston Health Department · Thursday, July 23, 2026
Houston's heat and humidity make it one of the moldiest cities in the country, and outdoor mold spores can trigger the same sneezing, congestion and asthma as pollen. The number below is theactual outdoor spore count measured today — reported in spores per cubic meter — with a breakdown of which molds are in the air.
Mold
HeavyLast 60 reporting days
Species breakdown
| Mold | Count |
|---|---|
| Ascospores | 6,907 |
| Cladosporium | 5,254 |
| Basidiomycetes | 1,810 |
| Penicillium/Aspergillus | 494 |
| Cercospora | 356 |
| Smuts/Myxomycete | 317 |
| Alternaria | 206 |
| Curvularia | 194 |
| Nigrospora | 117 |
| Dreshslera/Helminthosporium | 58 |
| Pithomyces | 36 |
| Algae | 30 |
| Periconia | 30 |
| Epicoccum | 18 |
| Torula | 14 |
| Rust | 12 |
| Oidium/Erysiphe(Powdery Mildew) | 10 |
| Spegazinia | 6 |
| Tetraploa | 4 |
| Stemphyllium | 0 |
Seasonal history — this year vs last
All trends →Daily counts across the calendar year, 2025 vs 2026.
Mold by genus
Why is mold so high in Houston?
Outdoor mold thrives on warmth and moisture, and Houston has plenty of both. Spore counts often run into the tens of thousands per cubic meter — far higher numbers than pollen — and tend to spike after rain, on humid mornings, and when fallen leaves and grass clippings are decaying. Unlike pollen, mold is not very seasonal here: it can stay elevated nearly year-round, easing mainly during cold, dry stretches.
The molds Houston tracks
The most common outdoor genera in the count are Cladosporium, Ascosporesand Basidiomycetes (the spores of mushrooms and shelf fungi), along withAlternaria — a well-known asthma trigger — plus smuts, rusts, Curvularia and others. These are outdoor air-sampling results; they don't measure mold inside your home, which requires separate indoor testing.
How to read the numbers
Because spore counts are so much larger than pollen counts, mold uses its own scale: in Houston a count in the low thousands is still graded Low, and it takes tens of thousands of spores to reach Heavy. See the FAQ for the exact thresholds, or thetrends page to see how spore levels have moved over the season.