How cleaning product chemicals called ‘quats’ may affect the brain

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The pandemic ushered in a cleaning frenzy at home, schools and work as many of us sprayed, wiped and disinfected our way through the crisis.

But widespread use of disinfectants and heavy-duty cleaners has also ushered in new research on “quats” – which stands for quaternary ammonium compounds (sometimes called QACs). Quats are a class of chemicals used in some household cleaners that kill viruses, bacteria and other germs by breaking down cell membranes.

In a 2023 review, more than two dozen researchers called quats “a chemical class of emerging concern.” Exposure to quats has been associated with asthma and an increased risk of chronic obstructive pulmonary disease in humans, as well as decreased fertility in mice.

Now, scientists at Case Western Reserve University School of Medicine in Cleveland have raised a new concern: They’ve found quaternary ammonium compounds to be potentially toxic to a type of brain cell. These cells, called oligodendrocytes, provide the fatty insulation (called myelin) around nerves, which allows neural signals to travel through the brain faster. The study also found that organophosphate flame retardants used in some household furniture appear to stunt the growth of oligodendrocytes.

“We’re not looking to say that there’s a direct correlation between exposure and human neurodevelopmental issues. We don’t have that data yet,” said Paul Tesar, the director of the Institute for Glial Sciences at Case Western Reserve and the principal investigator of the study. “But we have fundamentally shown, very rigorously, that oligodendrocytes have a specific vulnerability to these chemicals.”

There are hundreds of quaternary ammonium compounds, which can make it hard to identify the chemicals on an ingredient list. Quats often end with “ammonium chloride” or “onium chloride” in the name. One common quaternary ammonium compound in hand soaps, for instance, is benzalkonium chloride. Google can also help you figure out whether a particular ingredient in a cleaning product is a quaternary ammonium compound.

The American Cleaning Institute, a trade association for cleaning product makers, downplayed the findings. Brian Sansoni, senior vice president of communications, wrote in an email that the study “does not establish a causal link to any known or observed human health effect and should not be interpreted by readers to be predictive of possible health effects.”

“Surface disinfecting products, including those with quaternary ammonium compounds, are highly regulated and extensively evaluated for safety according to their approved uses,” Sansoni wrote. “Quats are a critical public health solution across homes, schools, health care settings and communities every single day. ”

The research on quaternary ammonium compounds doesn’t mean we should stop disinfecting our homes, experts say. But it’s good to be aware of the chemicals in your household cleaners, and to make informed decisions about which products you choose.

Erin Cohn, a graduate student in Tesar’s lab and the lead author of the study, said oligodendrocyte dysfunction is linked to various neurological conditions. In cases of multiple sclerosis, for instance, the body’s immune system attacks the insulation created by oligodendrocytes.

To study quats, the researchers used stem cells to grow human brain organoids – petri dishes of tiny, “millimeter-sized brain tissue” – intended to mimic early stages of brain development, Tesar said. And they found the quaternary ammonium compounds specifically killed oligodendrocytes but not the other cell types.

The researchers also fed the chemicals to young mice for 10 days. In autopsies, they found exposure to quats had “caused a selective loss of oligodendrocytes” in the brain, Tesar said.

“The science is clear that these chemicals have harmful effects on oligodendrocytes,” Tesar said. What’s not clear is whether “everyday exposure” to these chemicals affects the human brain.

Francisco Javier Quintana, a professor of neurology at Harvard University, said the brain is influenced “all the time” by the chemicals a person takes in. Although more study is needed, the results of the latest research suggest that exposure to quats could trigger disease in certain populations that are already genetically susceptible, he said.

“The quats could be acting as one little push, or the final push across the finish line,” Quintana said. “In most people, quat exposure probably does nothing. But if you carry the wrong genetic background, that might trigger disease development.”

Quaternary ammonium compounds have been detected in the breast milk of mothers, and they were higher in women who used disinfecting cleaning products. And a study of 43 people found that 80 percent had quats in their blood.

Libin Xu, an associate professor of medicinal chemistry at the University of Washington, said exposure to quats is “ubiquitous.” Almost every sample measured so far “has certain amounts of this compound, from very low to, occasionally, pretty high amounts,” he said.

In New York, researchers looked at quat exposure in shelter dogs, who live in caged areas that are frequently cleaned and disinfected. The study found that the feces of shelter dogs contained from two- to 18-fold higher concentrations of certain quats, compared with those of dogs who lived with their owners.

Terry Hrubec, a professor of anatomy and embryology at the Edward Via College of Osteopathic Medicine in Blacksburg, Va., said that, although we know quats can get into the body, “we know almost nothing” about their effects. “We’re just scratching the tip of the iceberg for what we know about quats,” Hrubec said.

Not all household disinfectants use quaternary ammonium compounds, and there are alternatives “that are equally effective,” with ingredients such as citric acid, ethanol and hydrogen peroxide, said Sarah Evans, an assistant professor of environmental medicine and climate science at the Icahn School of Medicine at Mount Sinai in New York.

If you’re concerned about the active ingredients in a disinfectant you’re using, open a window, and don’t spray or wipe with the product around children or pregnant people, Evans said. “Regular soap and water will kill most bacteria,” Evans said. “You don’t need a soap that has an added antibacterial chemical.”

Martin Wolf, director of sustainability for Seventh Generation, a maker of detergents and other cleaning products, said in an email that the company doesn’t use quats in its disinfecting products. The chemicals “have long been associated with respiratory irritation,” Wolf said.

Wolf said that, because the study was conducted on cultured cells in a lab, it’s not clear how it applies to the real-world use of cleaning products that contain quats. “It would be improper to dismiss the study out-of-hand,” Wolf said. “Rather, this should be seen as a caution to avoid use of the substances studied and to seek alternatives.”