"Stachybotyrs" known as black mold, is mostly common and a most common potent toxic mold to remediation companies as well. Most physicians have no mold toxin training which is sometimes overlooked by the severe effects it could have on patients physically especially with compromised immune systems such as children and the elderly.
Black mold requires water and not just high relative humidity to start to growth. Most common is sheetrock and wood especially exposed to outdoor conditions such as a construction site. HVAC air handlers and internally lined acoustical ductwork with fiberglass is another main culprit due to high moisture and dust that is not cleaned periodically. This makes for a perfect breeding ground for mold to thrive.
Typically when a homeowner has water leak behind walls, water will seep out. Even after cleanup, there may be an excess of water on the ground and behind the walls and if there is insulation between studs it will wick up the water causing mold to bleed through the wall over time. Of gassing bacteria will escape into the air causing musty odors and mold spores to go airborne and attach themselves to other items such as contents of the home.
Professional mold remediators should always isolate the area with a least 6 mil plastic walls to create and isolated area to keep contamination contained within that space. HEPA air scrubbers and negative air machines that vent outside are important to capture airborne mold during the remediation process. Before hiring someone to test or remediate your home or office, you should know some basics on mold testing and remediation. If your remediator has never heard of the EPA or OSHA guidelines, hire a different company. Read about basic mold remediation and clean up principles at www.epa.gov/mold.
Source: MoldBusters
