Soap may hold a dirty little secret in the form of a chemical called triclosan. Used in antiseptic hand soaps, shaving gel, toothpaste, deodorant and other hygiene products, a new study has found the chemical can weaken muscle contraction.
When researchers at the University of California at Davis exposed the individual muscle fibers of fish and mice to triclosan, they found it impaired the normal contraction mechanism. Both skeletal muscle and cardiac muscle no longer operated normally, and this was true when the mice and fish were tested themselves, or their muscle fibers were examined individually in a test tube.
Mice showed up to a 25 percent reduction in heart function measured within 20 minutes of exposure to the chemical, as well as an 18 percent reduction in grip strength -- yes, mice have grip strength -- for up to 60 minutes after exposure. Fish that swam in triclosan-tainted water for seven days performed worse on swimming tests than those that did not.
While the evidence for toxicity is largely based on animal studies, some experts have said that it might affect humans too.
"This is an interesting and potentially concerning finding, said Dr. Philip J. Landrigan, dean of global health in the department of preventive medicine at the Mount Sinai School of Medicine in New York City. "Many synthetic chemicals now known to be toxic to humans were first recognized as toxic in animal studies."
Landrigan said that exposure in the womb is of particular worry. "Early development is a time of particular vulnerability to toxic chemicals. Minute exposures at the wrong moment in embryonic or fetal development can have devastating effects. The great complexity of early human development creates windows of vulnerability, periods of heightened sensitivity to toxic chemicals that exist only in early life and have no counterpart in adulthood," he said.
Adding to the potential worry, previous studies have found that triclosan may alter hormone regulation in laboratory animals, or cause antibiotic resistance.
Not all experts believe the chemical is a problem because in it remains bound to blood proteins, which should in theory diminish its impact on humans. And manufacturers are adamant that there is no real proof triclosan is dangerous for humans. They're also quick to point out several recent studies that demonstrated its effectiveness in rd killing germs.
But some consumer groups and members of Congress have called for a ban on antiseptic soap products.
"If we adopted the precautionary principle, then we should remove it from consumer products. However, the United States chemical policy is included the Toxic Substances Control Act and calls only for voluntary testing of chemicals; therefore, the burden of proof of health effects falls on researchers, consumers and the chemical industry," said Dr. Adam Spanier, an assistant professor of pediatrics and public health sciences at the Penn State University Hershey Medical Center.
Both the Food and Drug Administration and the Environmental Protection Agency are currently reviewing the chemical's safety, but the FDA said it didn't have sufficient evidence for a ban.
"If studies continue to demonstrate adverse health effects of triclosan, then the FDA should call for its removal from consumer products," Spanier said.
Originally developed as a pesticide, tricolsan has also been added to common household items such as bedding, clothing, toys and trash bags, and has been for more than 40 years. Trace amounts of the chemical have been detected in waterways, as well as a wide variety of living organisms. In tests on humans it shows up in urine, blood, even breast milk. It is so prevalent that a survey by the U.S. Centers for Disease Control and Prevention found the chemical present in the urine of 75 percent of Americans over the age of 5.
This latest study was published in the Proceedings of the National Academy of Science.