What it is
Penicillium is famous as the source of penicillin antibiotics, but in homes it's a common allergen. Blue-green to gray, often appears in fuzzy patches.
Where it grows
Water-damaged materials - drywall, carpet, wallpaper, insulation. Also frequent on stored items: leather, fabric, books, paper, food.
Health impact
A common allergen. Contributes to respiratory irritation, sinus issues, and poor indoor air quality. Most reactions are inflammatory rather than infectious.
This species does not typically produce mycotoxins, though it can still cause allergic reactions and respiratory irritation.
Property risk
Aggressive spread. Damages drywall, carpet, and stored contents quickly. Often co-occurs with Aspergillus in water-damage scenarios - air samples that show high Aspergillus/Penicillium combined counts are a strong indoor-source signal.
When to test
If you see what looks like penicillium in your home - or if a lab report flagged it in your air samples - testing the affected area against an outdoor baseline is the most useful next step. The decision about remediation depends on:
- How much is present (spore count per cubic meter, or visible square footage)
- What's beneath it (porous materials like drywall and insulation usually need removal; hard surfaces can often be cleaned)
- Whether the moisture source is identifiable and fixable
Our approach
For confirmed indoor penicillium colonies, our process is the same as for any mold species: identify and stop the moisture source, contain the work area, remove what's compromised, HEPA-filter and HEPA-vacuum the surrounding area, dry everything, and verify with a post-remediation clearance test against the outdoor baseline.