America’s changing climate means flooding, heat and humidity are on the rise. These conditions are perfect breeding grounds for moisture-loving mold. However, sometimes mold can lie unnoticed, hidden under floors or behind wall panels, and the longer it’s left, the more damage it can do to health and homes. Understanding what mold smells like can increase the chances of early detection.
We spoke with three experts to learn how to identify mold’s distinct musty odor, how to find the source of the smell and what to do when you discover proliferating spores.
On This Page
What Causes Mold?
“The most common causes of mold in homes are related to dampness and moisture,” Rob Weitz, a leading mold consultant, says. He explains that mold is a fungus that thrives on wet surfaces, feeding on materials like wallboard, fabric, or even fruit. “Mold spores, which are [naturally] airborne, settle on these damp areas and quickly begin to grow,” he says.
While unaddressed water damage is a major cause of mold growth, other common causes might not be so obvious. “Areas prone to moisture, like kitchens and bathrooms, are particularly vulnerable due to activities like cooking, washing dishes, and taking showers,” Weitz says. “Basements and crawl spaces, which tend to be damp or poorly ventilated, are also common sites for mold growth.”
Mold and air quality expert Michael Rubino explains that high indoor humidity levels—above 60%—promote mold growth. He lists roof problems, gutter leaks, appliance malfunctions, damaged pipes, structural issues, and poorly maintained HVAC systems as other common culprits for mold problems.
What Does Mold Smell Like?
We asked the experts, “What does mold smell like?” Jack White, Senior Director of Technical Services at Rainbow Restoration, said it typically emits a musty, damp, earthy smell, often compared to a sour odor like wet clothing left in a washing machine. “Black mold can have a stronger, pungent odor,” he says.
Rubino explains that the musty smell, which he describes as “cigar-like,” is caused by the release of microbial volatile organic compounds (mVOCs) as mold grows and breaks down materials like damp wood, paper and fabric.
Not all mold growth has a distinctive smell, and different types of mold can produce variations in odor. However, any odor intensifies as the mold problem worsens. “This stronger smell indicates the colony is growing and releasing more gasses and byproducts, including spores and mycotoxins,” Rubino says.
How to Find the Mold
ARMAN ZHENIKEYEV/GETTY IMAGES
If you can smell mold but can’t see it, check areas prone to moisture, such as bathrooms, basements, HVAC closets, and behind sinks and appliances. Also, be vigilant for signs such as chipping or peeling paint, water stains, warped walls or flooring and dampness. “The mold is likely hiding in places that aren’t immediately visible, such as behind drywall, wallpaper, ceiling tiles, under carpets, or around pipes,” Weitz says.
“Chronic health issues with seemingly no underlying cause can also indicate mold indoors,” Rubino says. “Spores, fragments, and mycotoxins are small enough to be inhaled, ingested, and absorbed into the body, potentially leading to adverse health reactions in those exposed.”
Some common symptoms of mold exposure include runny eyes and nose, itching, coughing, sneezing, breathing difficulties and headaches. Often, the symptoms abate when you leave home and start again when you return.
When Should I Call a Professional About the Mold Smell in My House?
If you can smell mold but can’t see it, the mold problem is extensive or hard to reach, or you suspect serious black mold, it’s best to call a professional to help you deal with the problem safely and effectively. “The only way to know the exact type and risk of the mold present is through a mold test conducted by an environmental inspector,” Weitz says. He cautions against hiring the same company to carry out mold testing and any required remediation work, saying it’s a conflict of interest for a company to do both.
The EPA advises against handling mold removal yourself when the problem extends over an area larger than 10 square feet. However, even when the problem is affecting a smaller space, if you aren’t experienced in properly containing mold, you could make the problem worse if you don’t remove all the spores. “Mold spores are lightweight and can spread easily, making it easy to unknowingly cross-contaminate different parts of the home,” Weitz explains.
If you are experiencing extensive water damage in your home, you will likely need prompt, professional assistance to dry things out before mold forms. “All it takes is 24-48 hours on a wet surface for some species to begin growing,” Rubino says.
Rubino suggests hiring professionals to deal with mold in areas such as basements, attics, crawlspaces, ceilings and under carpets. “The extent of contamination might be hidden, potentially affecting the subfloor or framing behind the visible mold,” he says.
The Institute of Inspection Cleaning and Restoration Certification is a good place to start when looking for a suitably qualified mold remediator.
About the Experts
Michael Rubino is a mold and air quality expert, environmental wellness advocate and founder of HomeCleanse; email interview, Oct. 10, 2024.
Rob Weitz is the principal at RTK Environmental Group and a leader in the field of testing and consulting in mold. He is a certified microbial investigator with 30+ years of knowledge; email interview, Oct. 10, 2024.
Jack White is the Senior Director of Technical Services at Rainbow Restoration, a Neighborly company. Rainbow are rapid response experts in disaster restoration, including mold removal; email interview, Oct. 11, 2024.
Sources
EPA: “A Brief Guide to Mold, Moisture and Your Home” (2023)
