Triclosan is everywhere, but its days seem to be numbered.

Even if you've never heard of it, you've almost certainly come across triclosan. A highly effective antibacterial and antifungal ingredient, triclosan is found in all kinds of toothpastes, hand sanitizers, deodorants, mouthwashes, detergents, cleaning supplies—if you use household products, you're interacting with triclosan every day. So it's worrying that a new study, published in Science Translation Medicine on Wednesday, suggests that triclosan exposure could increase rates of colitis and colon cancer.

In the new study, led by a group of food scientists at the University of Massachusetts, Amherst, the research team fed different groups of laboratory mice—some healthy, some engineered or induced with some disease of some sort—water spiked with triclosan for three weeks, to emulate the levels found in people who had used triclosan-containing toothpaste for two weeks. All of those mice experienced exacerbated gut problems of some sort. Inflammation in the colon sprung up, leading to symptoms like rectal bleeding, diarrhea, abdominal pain, and even reduced lifespan.

It all comes down to what happens to your gut microbiome. It seems that triclosan devastated the diversity of bacteria found in the gut microbiome of those mice, and in particular killed off populations of Bifidobacterium, a "good" bacteria. The chemical transformed the intestinal flora into something antagonistic to the intestinal tissue, eliciting an inflammatory response from the body, as well as encouraging more aggressive tumor development in mice who were already battling colon cancer. This was only underscored by the fact that mice bred without gut bacteria did not experience inflammation even after exposure to triclosan.

Still, while distortions in the gut microbiome led to inflammation, it wasn't the only key factor. The researchers also noticed that other groups of mice lacking protein called Toll-like receptor 4, important in the inflammatory response of the body, were also immune to the deleterious effects of triclosan. Without the inflammation, triclosan exposure didn't do much to displease the gut.