A common class of antiseptic found in everything from mouthwash to spermicides has been found to impair the workings of our cells' mitochondria – the parts of the cell that convert glucose into other forms of chemical energy.
Concerns over the class of antimicrobial agents called quaternary ammonium compound has been so great, the US Food and Drug Administration (FDA) has already banned one of the chemicals from certain products and asked for more information on another.
Researchers from the University of California, Davis, tested two common forms of quaternary ammonium salts called cetylpyridinium chloride (CPC) and benzalkonium chloride (BAK) on human tissues under laboratory conditions.
This class of antimicrobial – commonly shortened to QUATS – is literally in just about everything. Soaps, body washes, lozenges, deodorants, toothpastes ... nearly anything you can think of as some sort of personal care product uses them to keep bacteria at bay.
Many QUATS have a rather nasty effect on microbes, ripping into their membranes in relatively low concentrations thanks to their fat-loving chemistry.
Because they aren't chemically altered by this action, the compounds retain their biocidal characteristics even after they've washed into the environment.
This has raised alarms in the past, where QUATS were found to cause reproductive problems in mice.
In 2016, the FDA ruled that the antiseptic compounds CPC and BAK were no longer recognised as safe to use in certain products, and made a call for more evidence to determine BAK's risks.
For their study, the researchers tested a collection of 1,600 FDA-approved and clinically approved antiseptics, additives, and drugs on two kinds of human cell line under in-vitro conditions.
In this case, those that contained QUATS were found to interfere with the workings of mitochondria, derailing an important transfer of electrons and inhibiting the organelle's ability to produce energy-carrying molecules called adenosine triphosphate (ATP).
Those that contained CPC were the most potent of the lot.
Just how this translates from a Petri dish to the real world of human and other animal bodies is yet to be fully established, but it's not looking positive, especially when complicated by other forms of medication.
"This raises concern because exposure to other mitochondrial-inhibiting drugs, such as rotenone and MPTP, is associated with increased risk for Parkinson's disease," says researcher Gino Cortopassi from UC Davis.
Not only do these antimicrobial agents lower the mitochondria's ability to pump out ATP, the researchers found that at certain concentrations they also interfered with the cell's response to an important reproductive hormone.
"Disinfectants that we are putting on and in our bodies, and using in our environment, have been shown to inhibit mitochondrial energy production and the cellular estrogen response," says Cortopassi.
In 2016, the FDA banned soaps and detergents that contained chemicals from a list of ingredients that included popular antimicrobials such as triclosan and triclocarbon, claiming there was greater potential for harm than benefits.
QUATS were being considered by some companies as possible safe replacements for these agents.
"This paper adds to the growing number of studies which find that QUATS may not be as safe as previously believed," says Terry Hrubec from the E. Via College of Osteopathic Medicine, who wasn't a researcher in this study.
The chemical category is a relatively large one, and not all QUATS compounds seem to behave in the same ways.
With the chemicals so prevalent that nearly all of us come into contact with them on a daily basis, more research is needed as soon as possible to tease out which could potentially be safe.
This research was published in Environmental Health Perspectives.