Hand soap has been center stage recently after evidence suggested it has been a large contributor to the current problem with antibacterial-resistant pathogens. Now scientists have put hand soap back in the hot seat, only for a different reason. Recent evidence suggests that triclosan, a common antimicrobial found in abundance in many hand soaps, is linked to liver fibrosis and the eventual growth of cancerous tumors.

Triclosan is one of the most common chemicals on the market. It is found in soaps, shampoos, toothpastes, and many other household items, including hand soap. In a recent study, researchers at the University of California, San Diego School of Medicine, exposed mice to triclosan for six months. According to the press release, this is roughly equivalent to 18 human years. Results showed that mice exposed to this chemical were more likely to develop chemical-induced liver tumors. The tumors were also more likely to be larger and develop at a higher frequency than those in mice not exposed to the chemical.

Although the study has not confirmed exactly how triclosan is tied to these tumors, research suggests it may be due to the chemical's tendency to interfere with the constitutive androstane receptor. This is a protein that helps the body to clear away toxin buildups. It’s believed that in order to compensate for the stress caused by the buildup of toxins, the liver cells may proliferate and eventually turn fibrotic. Years of exposure may lead the liver fibrosis to become tumors.

Unfortunately, triclosan is everywhere. Previous studies have found the chemical in the breast milk of lactating women and in 75 percent of urine samples taken from the U.S. general population. All this triclosan may mean bad things for humans.

"Triclosan's increasing detection in environmental samples and its increasingly broad use in consumer products may overcome its moderate benefit and present a very real risk of liver toxicity for people, as it does in mice, particularly when combined with other compounds with similar action," explained Dr. Robert H. Tukey, co-lead researcher on the project in the press release.

Although the Food and Drug Administration has not yet labelled triclosan as a toxin, according to their website, there is currently ongoing scientific and regulatory review of the chemical. However, Dr. Bruce D. Hammock, who also led the research, explained that not all amounts of triclosan are as dangerous to human health.

“We could reduce most human and environmental exposures by eliminating uses of triclosan that are high volume, but of low benefit, such as inclusion in liquid hand soaps," Hammock said. "Yet we could also for now retain uses shown to have health value — as in toothpaste, where the amount used is small."

According to the FDA, small amounts of triclosan in Colgate Total toothpaste have been proven effective in preventing gingivitis, without posing as much of a public health risk. If you would like to monitor how much triclosan is in your family’s products, this can be easily done. Due to FDA regulations, all over-the-counter products that contain this chemical must have it clearly labelled in its ingredients. The FDA advises consumers worried about using hand soap with triclosan to opt for washing their hands with regular soap and water.

Source: Hammock BD, Tukey RH, Yueh MF, et al. The commonly used antimicrobial additive triclosan is a liver tumor promoter. The Proceedings of the National Academy of Sciences of the United States of America. 2014.