Indoor vs. outdoor mold counts

The outdoor sample is not just background paperwork. It helps show what spores were naturally present in the local air at the time of testing.

Why the comparison matters

Buildings are not sealed ecosystems. Outdoor spores enter through doors, windows, ventilation, clothing, and normal air leakage. Finding some mold spores indoors is expected.

What can raise concern

Patterns worth investigating include indoor concentrations substantially exceeding the outdoor comparison, a species or group disproportionately represented indoors, or findings that align with a known moisture problem.

What a favorable ratio cannot prove

An indoor total below outdoor does not prove that every wall cavity is dry or that localized growth is absent. Air samples represent the air collected at one place and time.