Most molds reproduce by forming spores that disperse into the air in search of more food and moisture (a reproductive activity similar to seed dispersal from plants). Due to the diversity of mold in our environment, outdoor air normally always contains some level of these airborne mold spores.
A few types of spores are visible and anyone who has disrupted a puffball has witnessed millions of spores being released into the atmosphere. However, most filamentous mold spores are microscopic and therefore, invisible to the naked eye.
It is not uncommon to find hundreds or even thousands of mold spores per cubic foot of outdoor air. Some mold types, like Cladosporium, produce light and buoyant spores that aerosolize easily which is one factor in Cladosporium being frequently recovered in outdoor air tests.
Other types of mold, like Stachybotrys, do not easily go airborne and therefore, their spores are not frequently recovered in outdoor air tests. When actively growing, Stachybotrys spores are typically a wet, sticky mass that is not easily aerosolized. Some believe this organism's spores are like a cocklebur that hitchhikes on insects and rodents rather than traveling by air.
Light Microscope Image of
Not all spores produced by the organism are capable of growing a new colony. Microbiologists use the terms viable and non-viable to indicate their ability to reproduce and in lay terms, these spores are considered alive or dead.
Numerous factors (i.e. spore desiccation or other physical damage, etc.) influence a spore's ability to grow and comparative testing has shown a large percentage of airborne spores to be non-viable.
It is very important to recognize that spores retain their adverse health characteristics regardless of their ability to reproduce. In other words, non-viable spores are still allergens, contain toxins, etc. This trait not only has significance on exposure to molds, but also greatly influences testing methods.
Size Range of Spores
Things in the mold world are very small and dimensions are typically expressed in micrometers or microns (millionths of a meter).
Most fungal spores range from 1 to 100 microns in size with many types between 2 and 20 microns. People with good vision may see 80-100 micron particles unaided, but below that range, magnification is generally necessary.
To put things in perspective, you could place over 20 million five micron spores on a postage stamp.
A wonderful animation to depict sizes in the micron range can be viewed at the "How Big is..." page from CellsAlive!.
This small size has numerous impacts on dealing with mold. They are so tiny that they infiltrate our environments with air and they are essentially invisible so cleaning them up without special equipment and procedures is next to impossible. (It's tough to clean up things you can't see!)
Scanning Electron Microscope Image of
Since outdoor air normally contains some quantity of mold spores, infiltration of airborne mold into living and working environments occurs naturally. Therefore, even in structures without active mold colonies, the presence of airborne fungal materials is probable unless specialized air filtering systems are employed (i.e. clean rooms).
There is little we can do to stop nature's production of airborne mold spores, however, we can prevent mold from growing indoors. When these organisms are allowed to grow in a closed indoor environment, they can release millions of spores causing indoor levels to reach concentrations that are hundreds of times higher than outdoors...levels that can be detrimental to even healthy people.
Airborne mold spores are particles and generally settle out with time but they can be disrupted and re-aerosolized. They may also just sit quietly waiting for food and moisture.
Natural Airborne Mold Indoors
Many people have witnessed proof there are natural airborne mold spores indoors.
After inadvertently leaving a cup of coffee or food out for a few days, the resulting colony will be visible!
Breaking the Mold Triangle - Controlling Spores
Since mold spores are a natural component in air, they are essentially everywhere. In addition, spores are carried indoors on clothing, articles, pets, etc.
Eliminating mold spores from our indoor environments is virtually impossible without extreme measures of air and access control.