Mould & Mycotoxins

Moisture inside a duct system, or behind a wall the duct runs through, lets mould colonise where nobody can see it. Some species release mycotoxins into the air stream that moves through your home every time the system runs.

You can't tell what species you're dealing with by looking at it, and you can't tell whether a stain is mould at all without testing — a lot of what gets called "black mould" on sight isn't. That's why I test: surface and air sampling identifies which species are present and at what concentration, indoors versus outdoors, before anyone recommends a cleaning.

The usual cause is water — a leak, condensation, high humidity, or a duct that was never properly sealed. Fix the moisture and the mould doesn't come back. Clean it without fixing the moisture and it does.

Source: U.S. EPA, Indoor Air Quality. I'm a certified indoor air quality specialist, not a medical provider. I don't diagnose or treat health conditions.