Mold is a ubiquitous organism, a type of fungus found globally. Its presence indoors and outdoors is normal, as it plays a significant role in breaking down organic matter. Mold reproduces by releasing microscopic spores into the air. A mold count quantifies these airborne particles to assess their concentration within a specific environment, offering insight into air quality and potential contamination.
Understanding the Air Mold Count
The air mold count is a quantitative metric used to gauge the level of airborne mold spores within a defined volume of air. Results are typically reported in units such as spores per cubic meter (spores/m³). This number is tracked to assess potential exposure levels for building occupants.
Laboratories report two main types of counts. A total spore count includes all spores captured, encompassing both viable (living) and non-viable (dead) spores. Both are counted because even dead mold spores can trigger allergic reactions and respiratory symptoms.
The viable mold count only measures spores capable of growth and reproduction. These are reported as colony-forming units (CFU) per cubic meter, based on the number of colonies that grow when the sample is cultured. Total spore counts give a broader picture of contamination, while viable counts help identify specific species actively growing indoors.
Methods Used to Measure Mold Spores
Professionals use specialized equipment to collect air samples and generate the mold count number.
Non-Viable Sampling
This approach uses an impactor or spore trap cassette. Air is drawn through the cassette, and microscopic spores are captured on an adhesive surface. The sample is then analyzed under a microscope to count and identify all spores present. Non-viable sampling is often preferred for a quick assessment of the total airborne load.
Viable Sampling
This primary method collects spores onto a culture plate containing growth media. The plate is incubated in a laboratory, allowing only living spores to germinate and form visible colonies. This method is slower but allows for more accurate identification of specific mold species. Viable sampling can confirm the presence of a specific species.
Deciphering Mold Count Results
Interpreting a mold count relies on comparing the indoor air sample to an outdoor control sample. Since mold spores exist everywhere, a healthy indoor environment should have a lower or similar total spore count compared to the air outside. The types of mold found indoors should also mirror those found outdoors, indicating normal air exchange.
A problematic count occurs when the indoor spore concentration is significantly higher than the outdoor baseline. For example, if the outdoor count for Cladosporium is 1,000 spores/m³, but the indoor count is 5,000 spores/m³, this suggests an active indoor source. The presence of fungal components like hyphae, the “flowering bodies” of mold, also points to active growth within the building.
An indoor count is also problematic if it reveals the presence of species known as water-damage indicators, even at low concentrations. Molds like Stachybotrys (often called “black mold”) or Chaetomium are not commonly found in outdoor air. Their detection indoors signals persistent water intrusion and hidden growth.
What to Do About a High Mold Count
A high mold count signals an underlying moisture problem that must be resolved. The first step is to locate and fix the source of water intrusion, such as a leaky pipe, roof damage, or foundation issue. Mold will return if the moisture source is not permanently eliminated.
Next, the affected area should be isolated to prevent spores from spreading. Contaminated materials, especially porous items like drywall or carpet, must be removed and discarded under containment protocols. Professionals use specialized cleaning and drying techniques to ensure proper remediation.
Finally, long-term control involves reducing indoor humidity to inhibit future mold growth. Maintaining indoor relative humidity levels below 50% prevents the conditions mold needs to thrive. This is achieved by using dehumidifiers and ensuring proper ventilation in moisture-prone areas.