A new long-term study carried out by researchers at UC San Diego has revealed that an antimicrobial agent commonly found in soaps is linked to liver disease and cancer in mice.

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Hand soap, which has recently received bad press for its link to the rising issue of anti-bacterial resistance, is once again being fired upon for its link to liver fibrosis and cancer. Triclosan (TCS) is a common additive used in a variety of consumer products, including soaps, cosmetics and plastics. Due to its frequent addition to many common household items, levels of the chemical have often been detected in human body fluids as well as in the environment.

A long-term feeding study was carried out on mice in UC San Diego and produced evidence linking triclosan to liver disease. Upon long-term administration, hepatocyte proliferation increased, as well as fibrogenesis and oxidative stress, which are thought to be the main driving forces behind the development of advanced liver disease in mice. The chemical also strongly enhances hepatocarcinogenesis after diethylnitrosamine initiation which accelerates hepatocellular carcinoma.

The study was carried out on mice for 18 months, equivalent to 18 human years, and led to impaired liver function and tumors. The tumors were also found to be more severe and frequent when compared to mice not receiving the chemical triclosan.

So how does triclosan cause liver cancer in mice?

It was suggested that the chemical interferes with a member of the nuclear receptor family called constitutive androstane receptor (CAR). This receptor is important in the function of detoxification of foreign substances, for example drugs, within the liver. After the receptor senses drugs in the blood, it causes an upregulation of the expression of proteins which can then metabolize and excrete of them. If triclosan interferes with this receptor, the liver cells respond by proliferating and turning fibrotic over a period of time, ultimately causing liver fibrosis. Repeated exposure to triclosan and therefore fibrosis can lead to the formation of tumors.

Although this study was carried out in mice, the researchers believe it “demonstrates the TCS acts as a HCC tumor promoter and that the mechanism of TCS-induced mouse liver pathology may be relevant to humans. Hepatocellular carcinoma (HCC) is the most common form of liver cancer and although it isn't of very high prevalence in the United States, prognosis is usually poor and therefore any chemicals increasing the risk of developing the cancer should be avoided.

Bruce D. Hammock, PhD, who led the study along with Robert H. Tukey, PhD, at the University of California, said that 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. Yet we could also for now retain uses shown to have health value” as in toothpaste, where the amount used is small.