How mould exposure poses a dangerous health risk

Many moulds release poisonous substances called mycotoxins into the air, which can then be inhaled. Photo / Getty Images
Health symptoms caused by mould exposure can mimic a cold or feeling tired. If left untreated, mould can become life-threatening.
Thousands of Americans are returning to their homes after Hurricanes Helene and Milton brought severe flooding and damage to the southeast in recent weeks. In the aftermath, residents may be dealing with a familiar threat: mould.
Mould – a fungi – can begin to grow in a home 24 to 48 hours after water exposure. Mould is a natural part of the environment, but it is a health problem indoors, said Jae Williams, the director of communications for the Florida Department of Health.
“Mould isn’t necessarily going to kill you in 24 hours, but it certainly can have a pretty significant impact on your quality of life and on the health of your internal organs,” Williams said.
As climate change ramps up the frequency and intensity of flooding and storm events, experts said, mould is a growing health risk. We asked epidemiologists and other experts about the health effects of mould. Here are their answers.
Seeing or smelling mould is associated with developing asthma, exacerbating asthma, difficulty breathing, and upper respiratory symptoms such as sneezing, coughing or congestion, said Mark Mendell, an epidemiologist and affiliate scientist at Lawrence Berkeley National Laboratory. However, researchers are still working to understand the full extent of its health risks, he said.
For some people, symptoms are caused by an allergy to the mould itself, Mendell said, but those without allergies can still experience health issues. Researchers aren’t sure why.
A range of other health problems are being investigated for potential links to mould exposure, such as headaches, cognitive dysfunction, inflammatory bowel disease, autoimmune diseases and other types of inflammation, said Neha Solanki, a pulmonary physician at Cleveland Clinic.
One reason moulds could be harmful involves mycotoxins, poisonous substances released by certain kinds of moulds as a survival mechanism, and that can be inhaled.
Mycotoxins are known to have adverse health effects in the body when ingested. They are associated with the exacerbation of immunomodulatory conditions, and they have been linked to a wide range of health problems such as the development of cancer, neurological conditions, hormonal issues and liver cirrhosis (scarring of the liver), said Elizabeth Seymour, medical director of the Environmental Health Center-Dallas in Richardson, Texas.
Some experts, such as Dennis Hooper, clinical consultant and owner of Silver Gene, a Texas company that provides medical consultations related to mould and environmental exposures, believe mycotoxins can also be dangerous when inhaled.
But others, such as Mendell, point out that there is no evidence that inhaling mycotoxins causes harm to health.
“The issue of mycotoxins is controversial. There are some people who are convinced that we’re all being killed by mycotoxins from mould, but there’s not actually evidence to support this,” Mendell said.
Mould exposure is thought to contribute to “sick building syndrome”, a phenomenon where people get sick inside a specific building with no clear explanation, said Mary M. Johnson, a principal research scientist in environmental health at the Harvard T.H. Chan School of Public Health. Symptoms include headaches, fever, chills, fatigue, nausea, skin irritation, a cold and coughing, but the defining feature of the syndrome is that symptoms worsen when inside the building and improve upon leaving, Johnson said.
While other factors such as poor air ventilation could cause sick building syndrome, “mould is a major cause of it,” she said.
The indoor microbiome – a microscopic community of bacteria, viruses and fungi in the home – affects our health, experts believe. Research shows higher microbial diversity in the home is associated with a lower risk of asthma development.
But, mould growth is associated with a reduction in indoor microbiome diversity, said Jordan Peccia, a professor and the chair of the department of chemical and environmental engineering at Yale University.
“It appears that when mould grows in a home, it crowds out your exposure to all these other fungal spores,” Peccia said.
Mould can be much more dangerous for immunocompromised people, Peccia said, because they are susceptible to infections from mould, which can be life-threatening.
Mould comes in different colours, including yellow, green, white, blue and black.
The term black mould is a misnomer, Hooper said, because there are many species of mould that can be black, and some may be harmless. When people talk about concerns over black mould, they are usually thinking of a type of mould called Stachybotrys chartarum, which can produce mycotoxins, he said.
Regardless, Virginia Guidry, the occupational and environmental epidemiology branch head for the North Carolina Department of Health and Human Services/Division of Public Health, said that all moulds should be treated the same with respect to potential health risks and removal.
Common symptoms are a runny nose, watery eyes, sneezing and a cough, Seymour said. Some may also experience a scratchy throat or skin rash, she said.
Other symptoms include tiredness, brain fog, nausea and headaches, experts said.
“So many of the problems caused by mould seem to be less tangible, it’s very hard to get an eye on it,” Peccia said.
People who have an allergy to mould, those with existing lung conditions such as asthma, and immunocompromised people are at higher risk of mould-related health issues, Williams said. Outside these factors, some people appear to be more sensitive to mould, experts said, and it’s unclear why.
“The short answer is that everyone is at risk,” Williams said. “We should all be taking it pretty seriously.”
Where you live can increase your risk for mould exposure. Mould needs moisture to grow, so places with higher humidity are more susceptible to mould, Peccia said. Areas with extreme rainfall or frequent flooding are also at risk, he added.
Mould can infect the lungs and cause pneumonia, Guidry said, particularly if a person is immunocompromised.
The smell of mould in your home indicates that it may be actively growing and creating substances that can harm your health, Peccia explained. It will smell mildewy, stale or musty.
If your home is damp or has signs of water damage, you may have a mould issue, Mendell said, because mould needs moisture to grow.
A good mould inspector understands how water and air move through the home and will check different areas for mould, Peccia said. Many inspectors also use air samples, but usually “those are not really reliable,” he said, because most homes have some amount of mould spores in the air, which naturally comes in from outside. Test dust samples for mould and get the home thoroughly inspected instead, he recommended.
Some symptoms can be treated with antihistamines, nasal steroids, washing out the sinuses or allergy shots, Seymour said. In the long run, the best thing to do is to stop the exposure.
You have “to either clean up the mould or get out and avoid it,” Seymour said. “It’s the only way you’re going to heal.”
For some, the health effects seem to linger even after the mould exposure ends.
“I have also had patients – especially those with persistent exposure – who never fully recover symptomatically,” Solanki said.
Experts said it’s unclear how long the health effects of mould last and why some people seem to get permanently sick.
Remove visible mould and wet materials, Guidry said, and if you attempt to clean without professional help, wear personal protective equipment such as an N95 mask, goggles and gloves.
Dry out the space using fans or dehumidifiers, she said, and throw away carpet and padding with mould or water damage, because they are difficult to clean and dry.
Some items with mould growth can be cleaned with detergent or bleach, she said.
Locate sources of water or moisture in the home, Mendell said. “You have to fix the source of moisture because if you just remove the mould and the moisture is still there, the mould will come back,” he said.
Homes should be completely dry and clean before being reoccupied. If there’s any uncertainty about whether the mould is gone, call a professional, Guidry said.
“If you’re still seeing or smelling mould, there’s more work to do,” she said.