As cold and flu season has come around again, it is very important to wash hands frequently in order to minimize the number of germs being spread around. Not all soaps are created equally though, and some may have a dirty side to them. A new study found that regular exposure to large doses of triclosan—a common antimicrobial ingredient in soaps and toothpaste—can aggravate liver fibrosis and tumors in mice when given in conjunction with other carcinogens. Robert Tukey of the University of California, San Diego School of Medicine was senior author of the study’s paper, which was published in Proceedings of the National Academy of Sciences.
“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,” Tukey said in a press release.
The test mice in the study were given food that was 0.08% triclosan by mass every day for six months, which is the equivalent of 18 human years. This dose is hundreds of times higher than what a person would be exposed to through normal use of toothpaste and soap, but is perfectly in line for a study such as this. The test and control groups were both given diethylnitrosamine, a potent procarcinogen that can induce liver cancer.
The triclosan mice not only formed more hepatic tumors than the control group, but the tumors were also larger and grew more quickly. As the liver kicks into overdrive and tries to create new cells to replace the diseased ones, the organ becomes fibrotic and loses function, which happens much more readily in the triclosan mice. This is likely caused by a number of molecular pathways, some of which occur in humans. The researchers recommend investigating possible liver toxicity due to triclosan in human tissues.
Triclosan has been under fire for years as a potential endocrine disruptor in animal models that bioaccumulates in the environment, which may pose a risk to marine life. Though these studies have not yet shown cause of human disease at the low exposure dosages that come from hygiene products, triclosan has not been let off the hook. The FDA and EPA have called for further study to better understand the potential risk to human health and the environment.
This potential risk is highlighted by the fact that it hasn’t been shown to confer much, if any, advantage over certain non-antimicrobial products. If triclosan doesn’t even have a clear benefit to offer, it makes any risk seem fairly needless. The researchers report that traces of triclosan can readily be detected in the breast milk of nursing mothers, as well as in urine samples from 75% of adults. Triclosan does not bioaccumulate in the human body, but this does present some cause for concern and further investigation.
“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,” co-author Bruce Hammock of UC Davis added. “Yet we could also for now retain uses shown to have health value — as in toothpaste, where the amount used is small.”