What is Mold?
Molds (and mildew) are fungi. Fungi are neither plant nor animal but, since 1969, have their own kingdom. The fungi kingdom includes such wonderful organisms as the delicious edible mushrooms, the makers of the “miracle drug” penicillin and the yeast that makes our bread rise and our fine wines ferment. Biologically, all fungi have defined cell walls, lack chlorophyll and reproduce by means of spores. Approximately 100,000 species of fungi have been described and it is estimated that there are at least that many waiting to be discovered. The vast majority of fungi feed on dead or decaying organic matter – they are one of the principle agents responsible for the natural recycling of dead plant and animal life.
The most common fungi are ubiquitous within our environment and we are constantly exposed to them. For the most part, however, diseases caused by these common fungi are relatively uncommon and are rarely found in individuals with normally functioning immune systems.(1) Nonetheless, mold has recently experienced high profile press coverage. There are a variety of inflammatory press reports concerning lawsuits over air quality in homes, courthouses and other buildings; parental concerns regarding school classroom environments; home insurers refusing to cover mold damage; and widely distributed news reports on so-called “toxic mold.” But don’t panic. Mold can be managed effectively in most cases and this guide will help you do that.
There are 4 critical requirements for mold growth – available mold spores, available mold food, appropriate temperatures and considerable moisture. The removal of any one of these items will prohibit mold growth. Let’s examine each requirement, one-by-one.
|MAGNIFIED SPORANGIOPHORE OF THE PILOBOLUS — “THE SHOTGUN FUNGUS.” THE SMALL DARK KNOBS AT THE TOP OF EACH STALK CONTAIN THE SPORE SACKS THAT ARE “SHOT” UP TO 6 FEET INTO THE AIR TOWARD THE SUNLIGHT BY THIS UNIQUE FUNGUS.|
Mold Spores. Ranging in size from 3 to 40 microns (human hair is 100-150 microns), mold spores are ubiquitous – they are literally everywhere. There is no reasonable, reliable and cost-effective means of eliminating them from environments that humans inhabit. So, trying to control mold growth through the elimination of mold spores is not feasible.
Mold Food. If all three other requirements are met, almost any substance that contains carbon atoms (organic substance) will provide sufficient nutrients to support mold growth. Even the oil from your skin that is left when you touch an otherwise unsuitable surface, like stainless steel, or the soap residue left from a good cleaning will provide sufficient nutrients to support the growth of some molds. And many of the most common materials found in homes like wood, paper and organic fibers are among the most preferred of mold nutrients. Thus, eliminating mold food from your environment is a virtually impossible task.
Appropriate Temperatures. Unfortunately, most molds grow very well at the same temperatures that humans prefer. In addition, anyone who has cleaned out their refrigerator quickly realizes that temperatures close to freezing are not cold enough to prevent mold growth and temperatures that are much warmer than humans prefer, like those of the tropics, will grow abundant quantities of mold. Therefore, it is not feasible to control mold growth in our home environment through the control of temperature.
Considerable Moisture. Most molds requires the presence of considerable moisture for growth. Obviously, the word “considerable” is key here. The mycologists (fungi scientists) refer to “water activity” when describing the required conditions for mold growth. The various species of mold have different water activity requirements. A material’s “water activity” is equivalent to the relative humidity of the air that would be in equilibrium with the material at that material moisture content. The vast majority of mold species require “water activity” levels that are equivalent to material equilibrium moisture contents corresponding to relative humidities of at least 70%. In fact, the great majority of serious, large mold outbreaks inside buildings occur where porous, cellulose-type materials have literally been kept wet by liquid water or sustained condensation.
Human beings prefer humidities that are below the critical relative humidity for mold growth. Thus, of the four basic requirements for mold growth, moisture availability is by far the easiest mold growth requirement to control in environments that humans like to inhabit. As you will see from the remainder of this guide, and from the vast majority of the literature on mold control, the consensus regarding effective mold control strategies consists of the combination of reducing the availability of moisture and killing and removing active mold growth colonies.