Ubiquitous is my big word for the week. Webster's definition is “existing or being everywhere at the same time: constantly encountered.”
This describes the situation with molds. They don't magically appear or re-incarnate when conditions are right. They don't seep through solid walls as is often assumed. They are always there, floating in the air or carried in moving water, in a dormant state, just looking for the right combination of moisture, heat, and food sources to begin rapid growth.
Different molds like different conditions for propagation. Some like high moisture, some like active water infusion. They also have a variety of diets and temperature requirements. Some like the cellulose in sheetrock paper, others like wood in various degrees of decay and water saturation. Some like very warm temperatures, others like lower temperatures, but few will grow in cool or cold temperatures.
In fact, it is fairly easy to define the conditions that resulted in certain types of mold species being present. Very damp/wet conditions in the presence of sheetrock, is an ideal environment for the much maligned Stachybotrys. Damp, warm conditions over a lengthy period of time with a good amount of dust/dirt, is ideal for Penicillium.
The important point with molds that may produce some type of adverse effect on humans is the quantity . The quantity on surfaces that can be dislodged by physical contact and air movement, and the quantity of mold, floating free in the air, that can be inhaled.
The best way to evaluate the significance of the amount of indoor mold is to compare it to the amount of mold found in the outdoor air. The best measure of mold quantity is a comparison with outside levels, and total amount airborne. Unless conditions are right for indoor incubation, the mold levels should be equal to or less than, AND in the same general proportions as, outdoors.
If the mold levels are considerably above what is outdoors, or if there is a predominant mold not found in the same proportions as outdoors, something is going on inside that results in mold growth and propagation.
Measuring mold quantities is a controversial subject as well. Simply setting out a culture plate even for a measured amount of time is not an effective measurement tool. (A little science is worse than no science at all!). Mold and mold spores are so small that they don't readily settle unless they attached themselves to dust or moisture that permits them to reach a surface such as a sofa, floor or wall. An air sampling device that draws in a known quantity of air onto a growth medium is a much better test of what is in the air and what can be inhaled or become attached to skin or clothing.
Further, a surface sample or wipe test, carefully performed over a measured surface, is a better test of what is on a surface than on an open culture plate.
There are four different aspects of a mold that can come in contact with human beings. The first is the living mold itself—the live, growing plant. The second is the spore—a “seed” that can be in a dormant state for a long time waiting for the right conditions for growth. The third is the dead material—“the carcass”—of protein and other molecules that are present even when the mold is no longer alive and not capable of growing. The fourth are mycotoxins which are waste products generated by molds.
Each one of these materials: living mold, spore, carcass or mycotoxin, can adversely affect a human.
Mycotoxins seem to be in the public eye right now, there is little scientific evidence that mycotoxins are the predominant cause of Indoor Air Quality related illnesses.
It is just one of the factors in the mold life cycle that can adversely affect human beings.
There is much more than can, and needs, to be explained on this subject, but the first point to understand is that molds, specific to certain climates and environments, are always present. Usually in small quantities that do not affect most people. They do not magically appear but simply grow from a few spores when conditions are favorable.