The dirt on soap

Dear EarthTalk: Is it true that anti-bacterial soaps are no better at preventing infections than plain soaps and that they are actually harmful to the environment?

"" Avery Bicks, New York, NY

University of Michigan researchers reviewed numerous studies conducted between 1980 and 2006 and concluded that antibacterial soaps that contain triclosan as the main active ingredient are no better at preventing infections than plain soaps. Further, the team argued that these antibacterial soaps could actually pose a health risk, because they may kill beneficial bacteria and also reduce the effectiveness of some common antibiotics, such as amoxicillin. The study was published in the August 2007 issue of the peer-reviewed journal, Clinical Infectious Diseases.

These findings concur with earlier research conducted by Tufts University's Alliance for the Prudent Use of Antibiotics. The Tufts study concluded that overuse of triclosan could cause new strains of bacteria to develop, thus "changing the kind of bacteria in our houses to those that may actually be harmful or resistant to antibiotics"&

166;" said Tufts' Dr. Stuart Levy.

According to the non-profit group Beyond Pesticides, laboratory studies have found a number of different strains of mutated bacteria that are resistant to triclosan and to certain antibiotics. The organization also cites reports of triclosan converting into a carcinogenic class of chemicals known as dioxins when exposed to water and ultraviolet radiation. Besides cancer, dioxins have been linked to weakening of the human immune system, decreased fertility, altered sex hormones and birth defects.

If antibacterial hand soap is not effective at reducing infections, consumers may wonder about whether alcohol-based hand sanitizers may do a better job. Combing through different studies on the topic yields mixed conclusions. According to one study conducted at Colorado State University, alcohol-based hand sanitizers were as much as twice as effective as either regular soap or antibacterial soap at reducing germs on human hands.

A Purdue University study, however, contradicts these findings, concluding that while alcohol-based hand sanitizers may kill more germs than plain or triclosan-based soaps, they do not prevent more infections that make people sick. Instead they may kill the human body's own beneficial bacteria by stripping the skin of its outer layer of oil.

The best advice might just come from a study published in the journal Dairy, Food and Environmental Sanitation back in 1998, which concluded that washing hands thoroughly for 20 seconds or more with plain soap and warm water is by far the most effective way to reduce harmful bacteria, and as such remains our best defense against getting sick.

CONTACTS: Clinical Infectious Diseases, /CID/; Tufts' Alliance for the Prudent Use of Antibiotics, /med/apua/; Beyond Pesticides, .

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