When should I test for mold?

I’m not a doctor. I don’t play one on the internet either. Still, I am an environmental scientist, and experience has taught me that mold is often considered a problem only after it becomes visible or associated with a stench. Mold can exacerbate respiratory conditions such as asthma and allergies, stress the immune system, act as an irritant to eyes and skin, produce toxic substances called mycotoxins (from species of Penicillium, Aspergillus, Cladosporium, Fusarium, Stachybotrys chart arum), and cause migraines. If you have a chronic illness or neurological disease, or if your symptoms worsen when you visit a place where molds are present, having your home tested for mold may help reveal what’s going on.

People are often surprised to find mold growing in their home or workplace since they take special care to control water damage, humidity, ventilation, etc., but the truth is that molds thrive under the right conditions. Conditions conducive to mold growth include:
High humidity (>50%).
Poor ventilation (closed windows/doors).
Stagnant air spaces (low airflow).
Warmth (interior environments between 50°- 90°F or 10°- 32°C are optimal for most species of mold) nutrient-rich substrate (e.g., wood, wallpaper paste, dust particles that contain organic matter) lack of light.

Molds reproduce using spores that develop into new organisms germination—the production of a germ tube hyphal outgrowth—elongation of the hyphae by mitosis, often in coils branching—a secondary branch is produced at each point where a hypha bifurcates; every chapter ends in an enlargement termed a conidium fruiting body (basidiocarp or cleistothecium)—the mushroom-like structure that contains spores.

Laboratory analysis of air samples collected with specialized equipment is necessary to test for mold. Pieces can be captured onto Petri dishes containing unique adhesive materials (e.g., charcoal) to trap spores and prevent their dispersion through the air during sampling. Airborne fungi are quantified using quantitative PCR (polymerase chain reaction), which multiplies fungal DNA present in the air sample. Only a small volume of air needs to be sampled to achieve accurate results—in some cases, as little as 1-2 cubic feet (30-60 L) is required.

The Occupational Safety & Health Administration (OSHA) for guidance on assessing indoor mold includes information on sampling methods and analytical techniques. The US Environmental Protection Agency also provides published guidelines for performing mold assessments.
There are no standards or guidelines that specify how much mold may safely exist indoors without causing health problems; people vary widely in their susceptibility to mildew so that some individuals can tolerate exposure to massive quantities, whereas others will react adversely after relatively small exposures. If you suspect that your home or workplace has high mold levels, I recommend that you consult with an environmental professional who is experienced in indoor air quality testing.