As an antimicrobial ingredient, triclosan is a common component in shampoos, soaps, toothpastes, and other household items. Researchers from the University of California, San Diego School of Medicine, however, have found that long-term exposure to the ingredient has potentially serious consequences like liver cancer.

Using mouse models, researchers found that liver integrity was disrupted and liver function was compromised when the subjects were exposed for six months to triclosan, in a study led by Robert H. Tukey, Ph.D., a professor from the UCSD departments of biochemistry and pharmacology and chemistry, and Bruce D. Hammock, Ph.D., a professor from UC Davis.

In human years, that translates to about 18 years of repeated exposure to the chemical. Aside from being more susceptible to developing chemical-induced tumors in the liver, the mice also had larger and more frequently developed tumor compared with those that weren't exposed.

"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," said Tukey.

Their study suggests that triclosan doles out damage by messing with a protein tasked with clearing away chemicals from the body called the constitutive androstane receptor. The chemical buildup will then stress the liver, prompting its cells to multiply and then turn fibrotic over a period of time. Repeated exposure to triclosan pushes liver cells to continue turning fibrotic, which eventually promotes tumor growth.

Unfortunately, triclosan exposure is not hard to come by, with the ingredient present in most antibacterial products. Studies have even detected the chemical in 97 percent of samples of breast milk taken from lactating women and in almost 75 percent of urine samples from different people. Outside of soaps and household items, people may also be exposed to triclosan in nature. The chemical is also commonly detected in the environment, ranking one of the seventh most common compounds in streams all over the United States.

Before this study, triclosan was already being watched by the Food and Drug Administration due to recent reports where the chemical is said to impair contractions in muscles and disrupt hormones.

Partly funded by grants from the U.S. Public Health Service, the study includes Koji Taniguchi, Michael Karin, Ronald M. Evans, and Shujuan Chen as co-authors. Evans is from the Salk Institute for Biological Studies.

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