Triclosan, a chemical widely used in everyday products such as toothpaste, soaps, cosmetics, shampoos and detergent, has been found to cause liver cancer in mice.

New research involving laboratory mice, which was published in the journal Proceedings of the National Academy of Sciences (PNAS) on Nov. 17, showed that the commonly used antibacterial agent causes liver fibrosis and cancer, raising concerns about the chemical's safety in humans.

For the new study, Robert Turkey from the Laboratory of Environmental Toxicology of the University of California, San Diego and colleagues gave a group of mice food and water containing triclosan for a period of six months, which is equivalent to 18 human years.

The researchers found that the triclosan-fed animals were more likely to develop liver fibrosis, or hardened tissues, and cancer compared with the mice in the control group. They were also found to have larger and more frequent tumors with some also developing kidney fibrosis.

The researchers explained that triclosan, which was initially developed as an antibacterial ingredient for surgical scrub, may interfere with a protein known as constitutive androstane receptor. The receptor helps in detoxifying the body by flushing out foreign chemicals and, as a result, excess liver cells may multiply and with continued exposure, could eventually become tumors.

"Through a long-term feeding study, we found that TCS enhances hepatocyte proliferation, fibrogenesis, and oxidative stress, which, we believe, can be the driving force for developing advanced liver disease in mice," Turkey and colleagues wrote.

The mice that were used in the study were given 3 grams of triclosan per day. A gram of toothpaste only contains about 0.03 per cent triclosan. While the animals in the experiment were exposed to higher amounts of the antimicrobial ingredient than what most people encounter, there are concerns that people who are exposed to the substance for a long time could also be at risk of liver problems because the chemical may have similar effects on people.

Study researcher Bruce Hammock from the University of California, Davis Cancer Center said that exposure to triclosan can be reduced by eliminating high-volume uses of the substance offering low benefits, such as liquid hand soaps.

"Yet we could also for now retain uses shown to have health value -- as in toothpaste, where the amount used is small," Hammock said.

The study is not the first time that unwanted effects have been linked to triclosan. Earlier animal studies suggest that the substance can disrupt hormones in frogs as well as impair muscle function in fish and mice.

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