A fungus experiment in Dr. Joan Bennett’s lab at Rutgers University, New Jersey.

Mold Eats World

Toxic mold could be lurking behind your walls, inside your ceiling, and beneath your countertops, and our warming climate isn’t helping. But is this fungal explosion really the health risk we might think it is?

Long before the storm came, and floodwaters barged into her home, Joan Bennett remembers how she would go into the woods and find beautiful mushrooms. She dug them up, and, with her mother’s permission, planted the fungi in her family’s basement. It was the late 1950s, not long after her family moved from Bay Ridge, Brooklyn, to Westchester County, just north of New York City, and Bennett would have died if any of her friends from high school knew what she was doing. Through trial and error, Bennett learned that if you watered fungi like any old flowering plant, the organisms turned to slime and died. These clandestine attempts at cultivating mushrooms, trying to find the right conditions to make them flourish, were some of the earliest experiments she conducted—the prescientific days, she says, just messing around. In retrospect, it was one of her first steps on a lifelong path that would weave together a love of science and a love of fungi.

In 1963, while she was applying to graduate schools after getting a degree in biology from New Jersey’s Upsala College, Bennett received a course catalog from the University of Chicago. Flipping through the catalog to see what courses were offered by the botany department, the words “fungal genetics” caught her eye. She decided she wanted to be a fungal geneticist, a decision that put her at odds with the prevailing values of both molecular biology and womanhood at the time. Instead of finding a husband and having kids and doing, as she says, “whatever it was that women were supposed to do back in the 1950s,” or focusing on E. coli or phage—two trendy organisms in that field at the time—she became a scientist who studied mold.

Bennett in her lab at Rutgers.

Mold is a filamentous form of fungi that often resembles bruise-dark discolorations or cottony tufts of blue or white threads. There is, as the Centers for Disease Control notes, “always a little mold everywhere”—the types number in the hundreds of thousands, creating the flavor of blue cheese or appearing on shower curtains and loaves of bread. Over the past few years, though, the American public has increasingly seen mold as a toxic presence in their homes.

In that context, many people view mold as unsightly, unhealthy, potentially lethal. Mold is scary.

This is not a totally new reputation for mold, and it can be malevolent: certain species produce aflatoxins that can contaminate foods with some of the most carcinogenic compounds known to science. But for most of Bennett’s life, she has seen mold as a positive force. She recognizes its marvelous creations: cheese, soy sauce, rice wine, and all sorts of drugs, ranging from cholesterol-lowering statins to penicillin, the landmark antibiotic. Her relationship with it took a turn after Bennett, like so many of us, saw it blanket almost every surface inside her house, clinging to curtains and carpets, lurking inside and around walls and floors and everything in between. What Bennett saw, and experienced, changed the trajectory of her life. Thanks to our changing climate, we almost certainly will be living with more mold, in one way or another, in the future. “There’s so much more flooding than there used to be,” says Bennett, who is now 76 and a distinguished professor at Rutgers University in New Brunswick, New Jersey. “Rivers that haven’t flooded for 100 years are flooding every 5 years. The sea level is rising and it’s getting warmer.”

Bill Sothern, founder of Microecologies, at a client’s home that was found to have a mold problem.

It’s an overcast Tuesday in September, with the humidity nearing 100 percent and a category 4 hurricane called Florence barreling toward the Southeast United States. All signs point toward damp, moisture-laden conditions, ideal for incubating molds. Most people avoid both molds and the ecological crevices that they inhabit—underneath floorboards, below kitchen sinks, in basements and crawlspaces. But Bill Sothern seeks them out. Sothern, 72, is a former Army medic turned certified industrial hygienist, a New York-based professional who assesses the health and safety of homes and workplaces. Today he and I are speeding down the Brooklyn-Queens Expressway in a gold Volvo packed with metal canisters, vacuum pumps, and Air-O-Cell sampling cassettes. We’re heading to his first inspection site of the afternoon: an apartment occupied by a 35-year-old woman who claims she’s getting sick on account of sharing her living quarters with mold. “The landlord is going to be there,” Sothern warned me. “He is our adversary.”

Sothern runs Microecologies, a firm based in East Harlem that conducts indoor air-quality investigations. All day long, his cell phone rings as he fields calls from people in and around New York City asking him to verify their concerns about mold contamination. The vast majority of the time, Sothern says, he and his staff of ten find their clients’ health concerns about mold to be well-founded. Visible or measurable amounts of mold in damp, indoor environments have been associated with an increased risk of pulmonary disorders such as asthma, according to the World Health Organization. Beyond that, the field is dogged by controversy at every turn. Among mainstream scientists and industrial hygienists, the consensus is that although some molds produce the unhealthy substances known as mycotoxins, they are not ordinarily found in high enough concentrations to cause health problems in humans.

Sothern and a colleague put plastic over a wall found to have mold, in an attempt to contain potentially unhealthy airborne substances.
Try our new streaming service for free.
No algorithms. Just the best television + film hand-picked from around the globe.

“The dose that would be required to provoke a toxic effect in humans would be so high that it would be unreasonable,” Sothern explains. “That’s where the scientific mainstream is. You go outside that and you make a lot of people skeptical about you.” The process of getting rid of mold can attract opportunists, but he sees himself as one of the good guys—someone who acknowledges legitimate fears and collects evidence. That evidence, Sothern admits, is mostly anecdotal. Of the connection between health outcomes and infestations of Stachybotrys, which is commonly known as toxic black mold, he says, “There’s just no data.”

A little after 12 p.m., Sothern arrives at a newly renovated building. The landlord never shows up. The tenant, a lawyer, works at a large firm involved in environmental health and safety and climate change. (She agreed to be included in this story on the condition of anonymity.) She points out a patch of wood flooring that appears to be ever so slightly warped, and describes a waterfall pouring down an adjacent wall several months before our arrival. There are a few spotty discolorations that have appeared on the ceiling, she says, where a pipe burst. Periodically, the tenant stops speaking. “God, I’m getting a headache already,” she says. “I never had a headache before in my life. The headaches started with the mold.”

She says a naturopath recently detected mycotoxins in her urine, but Sothern pushes back, saying he’s skeptical about those tests, run by labs with questionable track records. Her symptoms could be caused by mold and mycotoxin exposure, but they could also result from anxiety and stress, or from something else entirely. Their conversation seems to reveal a recurring theme in discussions around mold: In the absence of an irrefutable diagnosis, all the uncertainties and unknowns have led to tension between the pull of fringe movements vying for legitimacy, and the push against the boundaries of respectable scientific research.

“I’m having all sorts of really bad neurological impacts,” the tenant tells Sothern. She acknowledges that it could be because of all the stress. “I’m saying the wrong thing. I’ll, like, go into a room or website and not know what I’m doing there, which is highly unlike me. I’m typically running on high vibrations.” She snaps her fingers.

“We do think of some of that stuff as being Stachybotrys-related, sometimes,” Sothern says. “Do you have the labs?”

“I do have the labs. There was not Stachy, or whatever. There was something else—some other types of mold. There was a ton,” she says. She lists off the names of several molds. “I think I’m getting a headache standing here.”

Sothern coughs. It seems like a sympathetic gesture—an affirmation that something doesn’t smell quite right.

A sample collected by Sothern from the ceiling of a client’s home.

Hundreds of millions of years ago, molds learned how to break down and decompose plant and animal tissue. Then Homo sapiens came along and started constructing freestanding shelters, and these huts and homes inevitably got wet and started to rot. Several thousand years later, people are still building structures out of plant fiber and cellulose material. Where you and I see particle board and paper-wrapped drywall, molds see an opportunity to feast. The problem, though, might not be them—it might be us. Modern humans spend an inordinate amount of time indoors. Several hypotheses (including one known as the “old friends” hypothesis) from evolutionary biologists, immunologists, and microbiologists suggest that modern sanitation and hygiene have thrown our immune systems out of whack, making us more susceptible to the microscopic bacteria and fungi that live in our midst. (According to estimates from the American College of Occupational and Environmental Medicine, 5 percent of the US population suffers from mold allergies.) Especially in recent decades, engineers and architects made strides in learning to seal off buildings from the outside world, often to save energy. Tightly sealed offices with reduced air circulation and myriad air pollutants—from the off-gassing of carpets and synthetic materials to photocopiers and, once upon a time, cigarette smoke—precipitated some of the first reports of “sick building syndrome,” a cluster of symptoms affecting people who lived and worked indoors.

By the 1990s, Joan Bennett was an expert on molds and a professor of molecular biology at Tulane University in New Orleans. She considered herself a skeptic of the idea that mold in homes and offices was making people sick. Despite anecdotal reports of dangerous mycotoxins and an entire cottage industry of mold abatement, Bennett took the prevailing scientific view: it is simply not possible for humans to inhale enough toxic mold spores to become sick, except in extraordinary cases—for example, if they work in a poultry barn, or are severely immunocompromised.

Bennett had even participated in a few legal cases, offering expert testimony on behalf of insurance companies looking to discredit sick building syndrome. “The situations vary, but there are people who are genuinely sick who sue their insurance companies,” Bennett tells me. “Sometimes they may be sick for entirely other reasons. We don’t know what the connection is. But to jump to the conclusion that a whole host of ailments is due to a fungus in your house hasn’t been scientifically proven.”

Bennett knew people were unwell. She just didn’t know how it would be possible to get sick from mold—until her own house became a petri dish.

A cross section of a ceiling that sustained water damage and now contains mold, in the home of one of Sothern’s clients.
Sothern collects a sample from some molding that revealed mold growth on the brick wall behind it.

The first time toxic mold exploded in the public consciousness was in 1997, three years after babies started showing up at the Rainbow Babies and Children’s Hospital in Cleveland with what was initially diagnosed as pulmonary hemorrhage. At the time, Dorr Dearborn, a pediatric doctor, saw a set of twins: one with major bleeding of the lungs, the other with no visible symptoms. Because the two lived in the same environment, he made a closer inspection and found that both babies were affected. He wondered if these same pulmonary problems were affecting a larger portion of the community. “We didn’t know how deep the iceberg was,” he says. “That scared us.” Dearborn called Centers for Disease Control and Prevention, and, within hours, an investigator from the CDC, Ruth Etzel, arrived. The investigation found that many of the affected infants, born to low-income families who were often African-American, lived in older homes on the city’s east side, and their homes frequently had water damage and, in particular, a species of Stachybotrys commonly called black mold. The CDC’s 1997 investigative report mentions one death, but the New York Times said mold was linked to six fatalities, and the Associated Press ran a headline calling the mold “The Baby-Killing Fungus.”

The report stirred up a media frenzy. In the ensuing years, an effort to update and clarify the initial findings only added to the controversy and confusion. By 2000, the CDC had added what amounts to a giant asterisk to the investigation, saying a panel of experts had “identified shortcomings” in its report and wanted to clarify the initial findings. Etzel did not claim that exposure to a specific type of mold caused illness, merely that there was a possible association; molds capable of making toxins were only one possible link between the babies’ health problems, since Stachybotrys was found in many of the infants’ homes. Nonetheless, the connection between mold and illness became the focus for both the press and the public. In its addendum, the CDC took pains to downplay the association between mold and the sick Cleveland patients. Dearborn still feels that the whole field of research has been “tainted” by the reinvestigation; he and others suspect the insurance industry was pulling some strings behind the scenes.

Rusty nails and warped wood, found in the flooring of one of Sothern’s client’s homes, indicate water damage and possible mold growth.

The CDC’s amended report did little to stop the public outcry, though. Molds have been blamed for contaminating Erin Brockovich’s home in Agoura Hills, California. Johnny Carson’s sidekick, Ed McMahon, attributed the 2001 death of his sheepdog Muffin to a “death mold” found growing in his 8,000-square-foot Southern California mansion. In 2001, a lawsuit filed in Austin set off a tidal wave of suits brought by homeowners against insurance companies, claiming household mold was making them sick; by 2002, the state of Texas—home to 8 percent of the entire American population—was responsible for 75 percent of all mold insurance claims nationwide. “Few Americans can be unaware of the toxic mold crisis and the crisis of toxic mold lawsuits,” writes Nicholas P. Money in the 2004 book Carpet Monsters and Killer Spores. “The ravages of the mold Stachybotrys, and the ensuing legal battles between residents of sick houses, parents with sick children, building contractors, landlords, and insurance companies, are regularly showcased in newspapers and on television programs.”

In the absence of a single, diagnosable medical condition that can be attributed to mold exposure, or any data about who it affects or how to treat all the different symptoms, confusion reigns. Doctors can be quick to dismiss patients’ symptoms, of, say, nerve pain or exhaustion as a psychosomatic response to stress or trauma. Many patients, in turn, go elsewhere for answers. The internet is full of self-proclaimed experts and personal-injury lawyers who speak in certainties and have a vested interest in convincing patients they have the answer. Some patients—or “moldies,” as they call themselves—have gone so far as to move to the desert in an attempt to avoid any contact with mold. Their approach has received little study and a significant side-eye from the medical and scientific establishment, incentivizing suffering people to double down on their own alternative diagnoses and treatments.

An experiment about fungi and its effects on flies in Bennett’s lab.
Visiting scholar Elsherbiny A. Elsherbiny conducts an experiment with fungi in the lab.

In August 2005, Hurricane Katrina made landfall on the Gulf Coast, flooding the city of New Orleans. Bennett and her husband fled with their three Brittany spaniels, and, after temporarily finding refuge at a country home in southern Louisiana, they drove north to New Jersey with their carload of dogs, uncertain whether their home would be destroyed or if Bennett would still have a job when they returned. Five weeks later, in October, Bennett returned to find that the floodwaters had receded from her neighborhood of Broadmoor, and although the half-century-old azaleas remained, the once-green bushes that lined her street had shriveled up and turned brown. Inside her and her husband’s home, things were even worse: almost every surface had transformed into a fungal utopia, cloaked in a fuzzy blanket of mold.

Unsurprisingly, Bennett had brought along petri dishes and sterile sampling equipment. It took her hours to sample her home. “The part of the story that I didn’t expect was that it made me feel sick to be in the house,” she says. A rug disintegrated in her hands and she lamented the destruction of her personal items, including a four-volume set of The Feynman Lectures on Physics. “The house smelled horrible, horrible, horrible,” she continues. “It had been closed up for a month, and these fungi had been in there eating my carpets, eating my books, eating my furniture, and putting out their metabolites—some of which were aroma compounds.”

Aroma compounds are what you might call whiffs of not-so-fresh air, what scientists refer to as volatile organic compounds, or VOCs—chemical compounds that evaporate, and can be emitted into the air by indoor furnishings or biological organisms. In the weeks following the hurricane, the gas vapors from mold had built up inside Bennett’s home, creating an odor unlike anything she had ever encountered in the lab. It was, she says, similar to the mustiness of an attic, but magnified many times over—like the difference between passing a dead skunk on the road and getting a shot of reeking stench sprayed on the family dog. “I started feeling sick,” she says. “I felt dizzy, so I’d go sit outside.” It was a bizarre twist, really: to watch (and smell) her house being eaten up by the same organisms she had studied all her life.

An experiment about fungi and its effects on flies in Bennett’s lab.
Petri dishes in the lab.

Slipping into scientific mode gave Bennett a way to deal with the disorienting intellectual and psychological shock of losing her home, her city, her sense of purpose. In the months after Katrina, Bennett admits that some strange thoughts crossed her mind—things that were not rational. For years, she had euthanized molds, killing them inside heated chambers designed to sterilize microorganisms in a steamy inferno; she found herself wondering if the creatures had figured out a way to exact retribution. Oh dear, she thought. All those molds I’ve autoclaved over the years—they’re coming back to haunt me. “A little embarrassing to admit this, but there were some dark moments,” she says.

Maybe feeling sick had nothing to do with mold, and everything to do with trauma. But it was during the long hours Bennett spent sampling and photographing her house that she remembered reading a hypothesis that suggested sick building syndrome might have nothing to do with toxins put out by mold—but it might have to do with the mold’s vapors.

On her second day inside her New Orleans home, she talked with a contractor she’d hired to clear it out. She had gone back there to take more samples, and one of the contractor’s employees, a man from Central America, asked his boss in Spanish: “Is she studying what makes us sick?” She found the employee’s question interesting, and provocative. At that point, she had no formal research project going; she just felt sad. It was filthy, and hot, and she noticed that a number of workers took off their gloves and respirators. The seeds of her future work were taking shape, even if she didn’t yet know its direction or purpose.

By 2006, Bennett had a teaching position at Rutgers University, and she and several colleagues published a study on some of the molds she had collected in New Orleans. The study appeared in the journal Proceedings of the National Academy of Sciences, and their research honed in on specific chemical compounds emitted by mold. After exposing fruit flies to these volatile compounds and comparing them to a control group, results suggested that mold’s off-gassing, or odors, disrupted the regulation of dopamine, a neurotransmitter critical to the brain’s reward system. This kind of disruption is thought to have a role in causing Parkinson’s disease. Fruit flies are a well-established model organism, like laboratory mice, but the results only hinted at the possibility that these noxious emissions could prove harmful to humans.

As she ventured into neurobiology—an entirely new field for her—in what Bennett describes as the twilight of her career, she knew that some might wonder if she had spun together a rope of a theory out of very little string. But her work was well-received in a small but growing field of study known as built environment, which focuses on the ecology of life found inside buildings. Bennett’s hypothesis that mold-produced vapors can impact people’s brains is credible, but it remains unproven; disorders of the central nervous system are notoriously difficult to diagnose. Most cases of Parkinson’s, the second most commonly diagnosed chronic neurodegenerative disorder in the country, are considered sporadic—cases are scattered, with no grand unifying pattern or single environmental risk factor to link them. (Or at least not one that scientists have been able to detect.) Inhaling mycotoxins sounds bad, but it’s hard to find irrefutable evidence that it actually has adverse effects on humans. “The bottom line is: I’m now willing to consider that people may be made sick by chronic exposure to mold vapors,” Bennett says. “Before I just was a skeptic, and now I’m thinking, Hmmm, it’s quite possible that for some people, some of the time, in certain circumstances, they may do that.”

Sothern investigates a client’s home.

The shift in the Earth’s climate has already begun to change the dispersal of microorganisms in the environment: pathogenic species of bacteria, including Vibrio cholera, the causative agent of cholera, have expanded from tropical regions into more temperate latitudes. Coccidioides, a soil-borne fungus that causes lung infections known as “valley fever,” are stirred up by dry, windy conditions, which appear to be intensifying. With more coastal development and more coastal flooding, mold growth is inevitable. Despite a $100 billion remediation industry, the vast majority of mold exposure probably goes unnoticed and undetected. The National Institutes of Health do not currently fund research on sick building syndrome. The Environmental Protection Agency and several other agencies fund research on indoor air quality, but the off-gassing of mold tends to go understudied and under-sampled. The physical labor involved in storm cleanup and remediation often goes to contractors who hire undocumented workers, adding to the difficulty in collecting epidemiological evidence.

Flooding is already a fact of life in coastal cities. Hurricane Sandy swept saltwater into New York’s subway system and flooded both private homes and public housing along the Atlantic seaboard. Hurricane Harvey deluged Houston. Hurricane Irma careened across the Florida Keys. Hurricane Maria tore across Puerto Rico. Communities in the Carolinas are still mopping up after Hurricane Florence. According to a search of the National Institutes of Health databases, there is currently one study on the health effects of mold in Puerto Rico, involving 50 homes, and another involving 50 flooded homes in Houston. Bennett sees a lot of missed research opportunities: after Hurricane Katrina, researchers arrived with sampling kits to test for heavy metals, while others went looking for cholera. “Almost no one,” she says, “came in and did a comprehensive scientific survey.”

Bennett says she would not be studying the potential health impacts of mold if she didn’t think there was something real at work. Her hypothesis about mold-generated emissions, which has not yet been rigorously tested or garnered widespread attention, might resemble a daisy chain of hypotheticals, an admixture of unreasonable fears and reasonable ones. What we do know is that certain biological organisms can and do proliferate indoors in the wake of coastal flooding, and some of these organisms are capable of producing volatile organic compounds. If these VOCs, in turn, are associated with neurodegenerative disorders, as it seems they are in fruit flies, then those links lead us to a question that almost sounds too bold to ask: could climate change actually mess with our minds?

Bennett is cautious. “There’s a lot of, you know, smoke around this,” she says. “There are people who claim that their mold-damaged houses are what has caused memory loss and neurodegenerative symptoms. To my knowledge, there’s no solid science backing that up, but I wish there was.” As we wait for science to catch up with coastal flooding, people like Bill Sothern keep working. Just this week, on October 10, Hurricane Michael made landfall in Florida, devastating whole towns. It has been called the strongest storm to ever hit the Florida panhandle. As of this writing, the damage in human lives and property is still be assessed. Wherever the clean-up goes, though, mold can be expected to follow.

Share this story