Aureobasidium pullulans
The pink-to-black yeast-like resident of wet surfaces
What it tells you about the building
Aureobasidium thrives on repeatedly wetted non-porous and painted surfaces — the classic organism behind stubborn dark staining on caulk lines and window gaskets. It signals surface-wetting patterns: condensation, splash zones, and ventilation shortfalls.
Why it matters in assessments
Mostly a surface and moisture-pattern indicator rather than a hidden-reservoir marker. Persistent recurrence after cleaning is the meaningful finding — it means the wetting pattern continues.
What remediation requires
Clean or replace colonized caulk and gaskets, then change the wetting pattern: ventilation runtime, squeegee habits in showers, and condensation control at windows. Replacing caulk without changing the moisture pattern restarts the clock.
Starts cream or pink and matures to shiny black; commonly the dark growth on bathroom caulk, window gaskets, and painted sills.
- Caulk, grout, and sealant lines
- Window gaskets and frames
- Painted damp surfaces
- Shower doors and tracks
State editions
Where this species shows up depends on where local climate and housing stock meet its moisture requirement. Read the local picture:
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