What it is
Alternaria is a common outdoor and indoor mold. Olive-green to brown, with a velvety texture.
Where it grows
Damp surfaces - shower stalls, around windows where condensation collects, basement walls, carpets, fabrics, food.
Health impact
One of the strongest mold allergens. Frequently linked to asthma exacerbations and hay-fever-like symptoms.
This species does not typically produce mycotoxins, though it can still cause allergic reactions and respiratory irritation.
Property risk
Visible growth on hard surfaces is usually surface-level. Growth on porous materials (drywall, fabric, carpet) usually means the material needs removal.
When to test
If you see what looks like alternaria 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 alternaria 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.