Triclosan reacts with chlorine, the most common disinfectant in municipal water systems, to form chloroform, a potential carcinogen. Scientists at the Virginia Polytechnic Institute and State University tested products with and without the chemical and found that antibacterial soaps could boost a person's exposure to chloroform 15 to 40 percent above the EPA's safe limit for tap water (80 micrograms per liter).
Over time, that amount could conceivably raise your risk of cancer, says Peter Vikesland, PhD, assistant professor of civil and environmental engineering at Virginia Tech and co-author of the study. He designed the experiment to simulate dish washing or showering—instances in which there's an extended period of contact. "Washing your hands with antibacterial soap for about 15 seconds probably is not an issue," he says. The research is preliminary, he cautions, "but the public should know the potential for this reaction."
Chloroform isn't the only possible risk. Triclosan has been linked to allergies and antibiotic resistance, and it's a major contaminant in U.S. waterways.
Plus the soaps seem to be a futile investment. In hospitals, the bacteria-killing properties of triclosan can prevent the spread of serious infections. But at home you don't need to kill the bugs; all you need to do is wash them down the drain. Ordinary soap and water does that every bit as well as antibacterial scrubs, according to a 2005 FDA advisory panel.