Concern about mold exposure in buildings continues to be a significant issue. The bottom line is that mold has been around for eons and is not going away. It will grow whenever and wherever buildings get wet and materials suitable for microbial growth are present. So what is mold exactly? This article provides a general overview on this topic.
[Updated 2019 – Content originally posted Sept. 5, 2014]
What is Mold Exactly?
Molds are members of the biological kingdom Fungi. This is distinguished, along with bacteria, from the other kingdoms. This is due to the way it grows and derives nutrients (through absorption rather than ingestion). There are over 100,000 identified species of molds.
It is likely that another 100,000 have yet to be discovered. Of these, only a relative handful of molds have been studied for their benefits and health risks.
Mold requires moisture to grow. In the presence of sufficient moisture, molds secrete enzymes. These enzymes break down the nutrient source (commonly cellulose for the molds that most frequently grow in buildings). This allows it to serve as food, which supports continued growth. The key to controlling microbial growth is to control the moisture.
Mold spores range from ~1 micron to over 100 microns in size. Most species associated with water-damaged buildings have spores that range from 2 to 10 microns in size.
What the Term Black Mold Really Means
One particular species of concern, Stachybotrys chartarum, is probably the best known mold found in water-damaged buildings. This species has been dubbed “black mold” or “toxic mold” in the news media, which in the public perception tends to make it public enemy #1.
Interestingly, though, a number of other species may be equally hazardous and considered black mold. There are hundreds of molds that are “black” in color. In fact, the color of many species varies with food source and other factors. As far as Stachybotrys being a “toxic mold,” there have been some cases where this group or other species have been suspected as the primary cause of death in a healthy individual, but these instances are highly rare.
Mold and Mycotoxins Indoors
There are several other groups of molds common in water-damaged buildings. They include species of the Penicillium, Aspergillus, Chaetomium, Trichoderma, and Cladosporium genera, to name a few. Many of these species may, when conditions are appropriate, produce chemicals called mycotoxins during their growth cycle. Mycotoxins may be capable of causing adverse health effects at very low concentrations.
Not all molds, however, produce mycotoxins. Those that do may only produce them some of the time. This is usually as a result of competition with other species for a food source indoors or when stressed out by other environmental factors. The application of biocides, such as bleach, may actually increase the production of mycotoxins as it could be considered a stressor.
Microbial Volatile Organic Compounds or MVOCs
What is that musty odor you notice when you enter a moldy building? That is actually gasses produced by active microbial growth. Microbial volatile organic compounds (MVOCs) are a byproduct of mold digesting its food and are the cause of these malodors. There are continuing studies related to MVOCs, many of which are known irritants. Exposure to MVOCs from molds has been reported to cause certain symptoms. These include headaches, nasal irritation, dizziness, fatigue, and nausea (taken from EPA Mold Remediation in Schools and Buildings). Research on MVOCs is still in the early stages. Time will tell how these metabolites impact occupant health.