How many of you have heard of triclosan [TCS]? I had not, until I spotted a paper out of the University of North Carolina, Chapel Hill, the University of Massachusetts, Amherst and Hong Kong Baptist University, on its potential toxicity, re: our gut bacteria. Apparently, triclosan is an ingredient added to many over-the-counter consumer products because it has antibiotic properties. Thus, you can find it in many toothpastes and, in the past, antibacterial soaps. On the FDA website, it is clear that there are some concerns over its use: “Some short-term animal studies have shown that exposure to high doses of triclosan is associated with a decrease in the levels of some thyroid hormones. But we don’t know the significance of those findings to human health. Other studies have raised the possibility that exposure to triclosan contributes to making bacteria resistant to antibiotics. At this time, we don’t have enough information available to assess the level of risk that triclosan poses for the development of antibiotic resistance.” However, according to a summary article about today’s paper, the FDA did demand it be removed from hand soaps sold to both homes and hospitals, because enough evidence had emerged by 2016 that its presence contributed to the growing issue of antibiotic resistance. That said, it is still ubiquitous in our environment, as it’s used in exercise clothing, yoga mats (to reduce bacterial growth), and toothpaste, where it is positively linked with a reduction in gingivitis.
It turns out that triclosan has also been targeted as a potential suspect in the growing epidemic of inflammatory bowel disease (IBD). The study I am describing today was done in an animal model, so again, this may or may not apply to us humans. However, these researchers have identified the specific bacterial enzymes that trigger triclosan’s harmful effects. And, they also have managed to block the enzyme’s action, which causes the intestinal damage see in those with IBD. According to the paper, “The incidence and prevalence of inflammatory bowel disease (IBD), the chronic inflammation of intestinal tissues, have risen dramatically in recent decades. In 2015, an estimated ~1.3% of U.S. adults (~3 million) were diagnosed with IBD, representing a 50% increase from 1999 (~2 million).” A 50% increase in incidence in only 16 years?! How scary is that!
Enzymes, microbial beta-glucuronidase (GUS) proteins, released by bacteria drive triclosan to damage the gut lining. The researchers used an inhibitor to stop the enzyme’s activity, and by doing so, stopped triclosan from exerting its negative effects. And while these experiments were conducted in rodent models, the scientists found that, “…TCS exposure in humans, the human stool samples also exhibited the same TCS metabolic profile as we observed in the animal experiments and contained a high abundance of free TCS.” They go on to point out that TCS is readily absorbed by the intestinal tract in humans, and they call for a reconsideration of its safety by officials, after their extremely significant findings: “…the safety of TCS and related compounds should be reconsidered given their potential for intestinal damage. Beyond TCS, it seems likely that gut microbial enzymes could contribute to the metabolism and toxicology of other chemicals, highlighting the critical importance of incorporating the microbiota in our understanding of environmental toxicology and mechanisms of disease.”
A 2017 paper, by the way, found that TCS actually alters the gut bacteria composition adversely, in a rodent model – likely also leading to adverse health effects: “Triclosan exposure has a profound impact on the mouse gut microbiome by inducing perturbations at both compositional and functional levels,” which may lead to “…novel mechanistic insights into triclosan exposure and associated diseases.” As noted above, IBD is already strongly linked to it.
So, if you, like me, are now determined to not use a toothpaste containing this ingredient, consider Jason’s, Tom’s, Nature’s Gate, Desert Essence, and believe it or not, Crest – a brand that actually brags about not using TCS in its products.
 Zhang, J., Walker, M.E., Sanidad, K.Z. et al. Microbial enzymes induce colitis by reactivating triclosan in the mouse gastrointestinal tract. Nat Commun 13, 136 (2022). https://doi.org/10.1038/s41467-021-27762-y
 Gao, B., Tu, P., Bian, X. et al. Profound perturbation induced by triclosan exposure in mouse gut microbiome: a less resilient microbial community with elevated antibiotic and metal resistomes. BMC Pharmacol Toxicol 18, 46 (2017). https://doi.org/10.1186/s40360-017-0150-9