Whether you’re coming home from an airport fluttering with international germs, a daycare full of sticky-fingered toddlers, or just a grimy office building, scrubbing your hands with bacteria-busting soap seems like a great idea. But the data that have washed up on the cleansers in recent years suggest that they actually do more harm than good—for you, those around you, and the environment.
Scientists report that common antibacterial compounds found in those soaps, namely triclosan and triclocarban, may increase the risk of infections, alter the gut microbiome, and spur bacteria to become resistant to prescription antibiotics. Meanwhile, proof of the soaps’ benefits is slim.
There are specific circumstances in which those antimicrobials can be useful, civil engineer Patrick McNamara of Marquette University in Milwaukee told Ars. Triclosan, for instance, may be useful to doctors scrubbing for minutes at a time before a surgery or for hospital patients who can’t necessarily scrub with soap but could soak in a chemical bath. Triclosan and triclocarban do kill off bacteria during long washes. But most people only clean their hands for a few seconds. “There’s evidence that there is no improvement with using soaps that have these chemicals relative to washing your hands under warm water for 30 seconds with soaps without these chemicals,” he said.
And the point hasn’t been lost on the US Food and Drug Administration. Though the agency ruled years ago that triclosan and other antimicrobials are safe, it’s now revisiting claims that the chemicals make soaps and other personal care products better. The FDA has asked antibacterial soap makers to send in data showing that their soaps beat out regular soaps at keeping people germ-free and healthy. The agency expects to announce this September whether the submitted data pass muster. If they don't, the companies that make up the $5.5 billion soap market may be forced to ditch the chemicals entirely.
In the meantime, however, researchers seem to be digging up more and more dirt on the chemicals, particularly triclosan. This antimicrobial is widely used in not just hand soaps, but body washes, shampoos, toothpastes, cosmetics, household cleaners, medical equipment, and more. And it’s just as pervasive in people as it is in homes and clinics. Triclosan easily enters bodies by ingestion (think toothpaste) or skin absorption. It’s commonly found in people’s urine, blood, breast milk, and even their snot.
A 2014 study led by microbiologist Blaise Boles of the University of Michigan in Ann Arbor tested 90 adults and found that 41 percent (37 people) had triclosan-laced boogers. Antimicrobial-snot paradoxically doubles your odds of having the potentially-infectious Staphylococcus aureus bacteria up your nose.
In rats exposed to triclosan, Dr. Boles and his colleagues found that triclosan exposure made it more difficult, not less, for the rodents to fend off Staph invasions. Triclosan seems to make the bacteria “stickier”—better able to adhere to proteins and surfaces. That stickiness could be why Staph is so good at hunkering down in the schnoz, setting the stage for future infections.
Other researchers have been looking at how triclosan and other antimicrobials may alter microbial communities further down from the nose—in the gut.
Microbiologist Thomas Sharpton of Oregon State University and his colleagues are currently studying triclosan’s effect on the gut microbiomes of zebrafish, a model organism for vertebrate development. Their preliminary data suggest that the antimicrobial causes swift, sweeping changes in the zebrafish gut microbiome, altering both diversity and community structure.
In another study, presented April 1 at the Endocrine Society's 98th annual meeting in Boston, researchers report that mother rats exposed to triclocarban—an antimicrobial used most frequently in bar soaps—passed on the chemical to their pups. The study, led by public health researcher Rebekah Kennedy of the University of Tennessee, Knoxville, also found that the chemical altered the microbiomes of both the mothers and the babies.
"Our research adds to the growing body of scientific literature suggesting unintended health consequences related to non-prescription antimicrobial use and will allow pregnant and nursing mothers to make informed decisions regarding use of these antimicrobial products," said Dr. Kennedy.
But, Dr. Sharpton cautions, we don’t know yet if such microbiome changes are lasting or if they spark health effects. “We’re really are in the beginning days of understanding how to interpret changes in the microbiome,” he said to Ars.
Still, previous studies have linked dampened diversity and rapid microbial changes from prescription antibiotics to health effects, such as a greater risk of intestinal infections. The results certainly warrant follow-up research, both Sharpton and Kennedy said.
While researchers continue to work out what antimicrobials do while they’re in people’s bodies, Dr. McNamara of Marquette University focuses on what the chemicals do once people pee them out or wash them down the drain. McNamara and his colleagues have been tracking both triclosan and triclocarban in wastewater treatment plants, where both chemicals can accumulate.
In a 2014 study, McNamara’s research team found that triclosan messed with the microbial communities that break down sewage, in some cases sabotaging their ability to digest the sludge. The chemical also caused a spike in the presence of a gene called mexB in the sewage microbes. This gene codes for a pump that allows bacteria to simply kick out tricolasn before it can kill them off. This pump, McNamara hypothesizes, also spits out common prescription antibiotics, such as ciprofloxacin. In experiments, bacteria with mexB were resistant to antibiotics, too.
In a January study, McNamara, his graduate student Daniel Carey, and colleagues found that triclocarban had the same effect as triclosan—it also disrupts the microbial communities that digest sewage and spurs bacteria to become resistant to drugs.
From wastewater treatment plants, these superbugs can leak out into waterways, wildlife, and potentially back to people, McNamara told Ars.
While some experts are hopeful that actions by the FDA and state regulators may nix the use of these chemicals in commercial products, McNamara thinks consumer choices may be the most powerful way to reduce use of the chemicals. People could use regular soap or ethanol-based sanitizers and have effective, less risky cleansers, he said. “There’s a way that we can still keep our hygiene without having these extra chemicals.”