Mold Spores · Canairy

What it is

Mold is a kind of fungus that grows on damp organic surfaces. It reproduces by releasing microscopic spores (usually 2 to 100 micrometers across) that float through indoor and outdoor air. Common indoor genera include Cladosporium, Aspergillus, Penicillium, Alternaria, and Stachybotrys (often called black mold). Some molds also release volatile organic compounds (called mVOCs) that produce the musty smell people associate with water damage, and a smaller number produce mycotoxins.

Where it comes from

Mold needs moisture, organic material to feed on (drywall, wood, carpet, paper, dust), and a temperature between roughly 40 and 100 degrees Fahrenheit. Indoors, mold grows wherever water lingers: behind leaky pipes, under sinks, around poorly sealed windows, in bathrooms with weak ventilation, in basements with high humidity, and behind walls after flooding. Outdoors, spore counts rise in late summer and fall, especially in humid regions and after rain.

According to EPA, the only practical way to control indoor mold is to control moisture. Indoor relative humidity above 60 percent supports mold growth on many surfaces; ASHRAE recommends keeping indoor RH between 30 and 60 percent.

Health effects

Most healthy people are not seriously harmed by typical indoor mold exposure, but reactions vary. Allergic responses are the most common: stuffy nose, sneezing, itchy eyes, sore throat, coughing, wheezing, and skin rash. People with mold allergies, asthma, or weakened immune systems can have severe reactions. CDC notes that exposure to damp and moldy environments is linked to upper respiratory symptoms, coughing, and worsening asthma in sensitized people.

Less common but serious conditions include hypersensitivity pneumonitis (from heavy chronic exposure, mostly occupational), allergic bronchopulmonary aspergillosis in people with asthma or cystic fibrosis, and invasive fungal infections in people who are immunocompromised. Mycotoxin exposure from indoor mold has been a subject of debate; the scientific consensus is that inhaled doses in typical water-damaged homes are usually far below toxic thresholds, but health effects from chronic dampness exposure are real and well documented.

How it's measured

There is no federal exposure limit for indoor mold and no agreed-upon safe airborne concentration. Outdoor spore counts often range from a few hundred to tens of thousands of spores per cubic meter depending on season and location. Indoor concentrations are usually compared with outdoor levels measured the same day; indoor counts substantially higher than outdoor (especially of species not common outdoors) suggest an indoor source. Air sampling pulls a known volume across a sticky slide for direct microscope counting, or onto agar for culture. Bulk and surface samples test specific materials.

For most homeowners, visible mold or a persistent musty smell is reason enough to act, no testing required.

What you can do

Fix water leaks within 24 to 48 hours. Run bathroom and kitchen exhaust fans during and after showers and cooking. Use a dehumidifier or air conditioner to keep indoor RH below 60 percent (ideally 30 to 50). Insulate cold surfaces to prevent condensation. Clean small areas of mold (under 10 square feet) with detergent and water, dry thoroughly, and wear gloves and an N95. For larger areas, sewage damage, or mold in HVAC, hire a remediation contractor who follows EPA or IICRC S520 guidance. HEPA air purifiers reduce airborne spores but do not fix a moisture problem.

Sources

This article is for educational purposes only. Canairy does not provide medical advice, diagnosis, or treatment. Talk to a qualified health professional about your specific situation.