Molds are fungi that exist almost everywhere in the outdoors – and inside, they’re a common component of household dust. But mold can become a nightmare when there’s a large amount and it’s busily forming colonies in your home.
Like any pollens, dust and other airborne allergens, mold can cause a host of reactions in people who are sensitized, from itchy, watery eyes to sinus problems to full-blown asthma .
But according to Dr. Ginger Chew, an epidemiologist with the U.S. Centers for Disease Control and Prevention, besides triggering allergic reactions, molds can also cause breathing problems and other irritant effects in people who are not allergic.
In rare circumstances some molds can be infectious or toxic; and as they are growing, these spores can produce microbial volatile organic compounds, or mVOCs, which can trigger the same kinds of reactions as VOCs that off-gas from paints  and other household chemicals.
Those tiny VOCs can hitch rides around your home – and even slip right out of wall cavities and into your home. “VOCs can permeate through porous surfaces very easily because they are volatile,” Chew explains. “And a lot of the things we think are non-porous really aren’t – like drywall.”
So how much exposure to these homewreckers is OK?
There are guidelines and international standards, but Chew says levels that are deemed “safe” can still pose problems for those with mold allergies or sensitivities – and an individual’s condition can get worse with prolonged exposure.
“People who are allergic or have asthma mount a quicker and more intense immune response and become sensitive to even smaller concentrations.
“So it’s a moving target,” says Chew, who explains that the irritant-type reactions (such as pneumonitis or lung tissue inflammation) are usually associated with people who get big hits of mold on the job, and on a regular basis.
But if a family keeps having to re-caulk a moldy bathtub or is ignoring a mold problem altogether, “it can also be happening in a home.”