Triclosan was in the news again this week as researchers in California published a study showing that the antimicrobial agent causes liver fibrosis and cancer in laboratory mice.

The scientists from UC Davis and UC San Diego said that their findings are relevant to human health because long-term exposure to the chemical may cause similar changes in people.

Triclosan is a synthetic compound not found in nature. It is added to a wide range of soaps, shampoos, toothpastes and other consumer and household products, but there have been concerns about its safety for a number of years and the ingredient is currently under review by the U.S. Food and Drug Administration.

The latest study showed that triclosan disrupted liver integrity and compromised liver function in mouse models. The researchers found that mice exposed to triclosan for six months — which is equivalent to around 18 human years — were more susceptible to chemical-induced liver tumors. Their tumors were also larger and more frequent than in mice not exposed to triclosan.

This is thought to be caused by the antibacterial agent interfering with the constitutive androstane receptor, a protein responsible for detoxifying foreign chemicals in the body. To compensate for this stress, liver cells proliferate and turn fibrotic over time. In turn, that can eventually promote tumor formation, the University of California reported.

"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," commented Professor Robert Tukey of UC San Diego.

The study was led by Tukey, together with Professor Bruce Hammock. Their findings have been published in the Proceedings of the National Academy of Sciences.