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Is indoor mold harmful?

With more than 100,000 varieties, mold is a necessary fungus for our ecosystem’s survival. It thrives in warm, damp, dark, and poorly ventilated areas. Mold assists the cycle of life by decomposing organic matter, such as fallen fruit from a tree, which is then recycled into the soil. We encounter microscopic mold spores just about everywhere, indoors and out. Outdoors, mold resides on grass, leaves, wood, flowers, and in the air. As such, we often track mold into the home, and it transfers to floors, countertops, furniture, and carpets.

Indoor mold is most commonly found in basements, kitchens, bathrooms, and anywhere a spill, leak, or flood has not completely dried. You may have also seen mold growing in a forgotten latte mug or on fruit left on the counter for too long. Mold is made of microscopic spores and is not always visible. When we perform normal household chores, the microscopic spores take flight, contaminating the air and settling into the home's ventilation system. Mold grows quickly and infiltrates porous surfaces such as sheetrock. A mold contamination may mean major household cleanup, damage, repairs—and, in extreme cases, full house demolition.

Is indoor mold harmful?

Mold exposure in high concentrations and certain toxic molds cause allergies, respiratory distress, chronic respiratory illness, and even death. Here are common symptoms of mold-induced respiratory illness versus mold allergy:

Mold-induced respiratory illness

Symptoms of mold-induced respiratory illness, or hypersensitivity pneumonitis (HP), can be acute or chronic. Acute mold-induced illness typically has a sudden onset of symptoms that appear in the first 12-48 hours after exposure. Symptoms typically dissipate over a couple of days once the person removes herself from the mold source.

Chronic mold-induced illness can have a sudden onset of symptoms or build over time. Chronic respiratory illness symptoms last long-term—weeks to years—even if the person distances herself from the mold source. Most cases of chronic mold-induced illness, as with cases of Farmer’s Lung, are the result of repeat or long-term mold exposure. Still, chronic respiratory illness may develop after just one encounter with mold.

Symptoms of mold-induced respiratory illness

impaired respiratory function

impaired motor function

painful breathing












cold/flu-like symptoms

Mold allergy

Mold allergy tends to be acute and dissipates once the person distances herself from the mold source. A person who experiences an allergic reaction to mold may do so after one encounter, even if the person never experienced a mold allergy before. Studies also reveal a correlation between mold exposure in infancy to life-long mold allergy.

Symptoms of mold allergy

itchy skin

rash or skin irritation

watery eyes

burning/tender eyes

runny nose



clear mucus

dry cough

Harmful effects of mold exposure

Most of us touch and inhale trace amounts of mold, mostly invisible to the naked eye, every day without issue. Mold produces mycotoxins, the chemical bi-products released when mold decomposes organic matter. Certain mycotoxins cause severe respiratory illness and even death, as with cases of black mold exposure. Even brief mold exposure may cause allergies and impact the overall health of your eyes, skin, lungs, and nasal passages.

Safety precautions, such as wearing a mask over your nose and mouth, greatly reduce your risk for respiratory illness and allergy. People with vulnerable immune systems—infants, the elderly, the ill, those who are pregnant, and those with allergic sensitivities—are at the highest risk of mold-induced illness. Anyone who lives in a damp or tropical region, spends time in a closed environment recently subject to storm flooding or a plumbing flood, or a space undergoing renovations should take precautions to prevent mold exposure. You can safely prevent and remove mold in small areas.

In 1994, researchers in Cincinnati investigated a cluster of sudden infant deaths from respiratory failure and hemorrhaging. The study revealed that the infants were exposed to mold. The American Academy of Pediatrics reports that “the infants with pulmonary hemorrhage were more likely to have resided in homes with major water damage from chronic plumbing leaks or flooding.” (1) Similar studies report that up to one-third of children are allergic to mold, revealing that mold exposure in infancy is the likely catalyst for life-long mold allergy.

Hypersensitivity Pneumonitis (HP) is a harmful condition common in the farming population. The condition is colloquially termed, “Farmer’s Lung,” and results when the person inhales mold from hay and crops. Cases of HP may be acute and turn chronic after repeated exposure to the mold. While HP can affect anyone who comes in contact with mold, particularly home contractors, farmers account for 30 percent of all respiratory illness cases. HP forces many farmers out of their trade. In severe cases, the condition results in death from pneumonia or impaired respiratory function.


  1. American Academy of Pediatrics, “Toxic Effects of Indoor Molds

  2. American Lung Association, “Hypersensitivity Pneumonitis

  3. Centers for Disease Control, “Facts About Stachybotrys Chartarum and Other Molds

  4. Environmental Protection Agency, “Mold Cleanup in Your Home

  5. National Ag Safety Database, “Farmer’s Lung

  6. Parents, “Mold: The Hidden Allergy Problem

  7. Web MD, “Mold Allergy"

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