Germ-zapper in soap causes liver tumors in mice

"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," Bruce D. Hammock says. "Yet we could also, for now, retain uses shown to have health value—as in toothpaste, where the amount used is small." (Credit: iStockphoto)

Long-term exposure to triclosan, an antimicrobial agent commonly found in a broad array of soaps, shampoos, toothpastes, and other consumer products, may have potentially serious health consequences, report researchers.

Data from a new study shows that triclosan causes liver fibrosis and cancer in laboratory mice through molecular mechanisms that are also relevant for humans.

The study appears in the journal 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,” says Robert H. Tukey, a professor in University of California, San Diego’s departments of chemistry and biochemistry and pharmacology.

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The researchers found that triclosan disrupted liver integrity and compromised liver function in mice.

The mice exposed to triclosan for six months (roughly equivalent to 18 human years) were more susceptible to chemical-induced liver tumors. Their tumors were also larger and more frequent than those in mice not exposed to triclosan.

The study suggests triclosan may do its damage by interfering with a protein called the constitutive androstane receptor, which is responsible for clearing foreign chemicals from the body.

To compensate for this stress, liver cells proliferate and turn fibrotic over time. Repeated triclosan exposure and continued liver fibrosis eventually promote tumor formation.

Triclosan in breast milk and urine

Triclosan is perhaps the most widely used consumer antibacterial. Studies have found traces of it in 97 percent of breast milk samples from lactating women and in the urine of nearly 75 percent of people tested. Triclosan also is common in the environment: It is one of the seven most frequently detected compounds in streams across the United States.

“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,” says study co-leader Bruce D. Hammock of the department of entomology and nematology, and the Comprehensive Cancer Center at University of California, Davis.

“Yet we could also, for now, retain uses shown to have health value—as in toothpaste, where the amount used is small.”

Triclosan is already under scrutiny by the FDA, due to its widespread use and recent reports that it can disrupt hormones and impair muscle contraction.

Additional coauthors contributed from UC San Diego and the Salk Institute for Biological Studies.

Tukey and Hammock are directors of National Institute of Environmental Health Sciences Superfund Programs at their respective campuses.

This research received partial funding from US Public Health Service grants.

Source: UC Davis