December 23, 2005
Cleaning Up Antimicrobial Hand Soaps
Each day, millions of Americans use antimicrobial soap products to wash their hands. Rolf U. Halden, PhD, PE, an assistant professor in the Department of Environmental Health Sciences at the Johns Hopkins Bloomberg School of Public Health, studies the chemicals used in antimicrobial consumer products. In October, he served as a member on the U.S. Food and Drug Administration’s (FDA) Center for Drug Evaluation and Research panel, which was convened to examine the benefits and hazards of antiseptic hand soaps and body washes marketed for consumer use. The Office of Communications and Public Affairs spoke with Halden about the conclusions of the panel members and the issues surrounding antimicrobial soaps.
Office of Communications and Public Affairs: What are some of the concerns over the use of antimicrobial soaps?
Rolf Halden: One concern is that antimicrobial hand soaps may contribute to the rise of germs that are resistant to treatment with antibiotics. Most antimicrobial soaps use either triclosan or triclocarban as an ingredient to kill microorganisms. Triclosan is labeled a biocide, which means that it uses a non-specific mode of action to kill microbes. It is thought to destroy biological structures at random. Triclocarban resembles triclosan in structure and function.
Non-specific cell damage is not the only mode of action, however. Recent investigations demonstrated that triclosan also targets a specific site in the fatty acid synthesis of microorganisms. These studies can help to explain why laboratory bacteria exposed to triclosan were observed to develop cross-resistance to 7 out of 12 antibiotics evaluated—a finding interpreted by some scientists as a red flag and a harbinger of more drug-resistant microbial infections in humans.
OC&PA: Do these chemicals have negative environmental impacts?
RH: Triclosan has been detected in fish and in breast milk. This is not a big surprise since it shares similarities with other chlorinated organic pollutants, such as dioxin, PCBs and DDT. My laboratory group has detected triclosan and triclocarban in surface water, aquatic sediments and in municipal sludge, a sewage treatment by-product that is used extensively as agricultural fertilizer. Due to their persistence, both chemicals are widespread environment pollutants, detectable in about 60 percent of U.S. streams.
Triclosan is a pre-dioxin. It contains small quantities of toxic dioxins and can be converted to form additional dioxins when irradiated with sunlight. Triclocarban is a suspected carcinogen that can disintegrate to release two carcinogenic substances for each molecule converted.
OC&PA: If these compounds are harmful, why would they be allowed in soap?
RH: When assessing the health risks of antimicrobial chemicals for use in cosmetics and other personal care products, we usually look at dermal exposure, absorption through the skin, which is very limited and thus considered safe given the data available today. However, since these chemicals are persistent environmental pollutants, other potential routes of exposure may exist. Antimicrobials may function as “chemical boomerangs” that, following disposal into wastewater, can come back to us contained in food and drinking water. This route of exposure is less well understood and needs to be studied further. While the “useful” lifespan of these compounds is measured in seconds or minutes, their environmental half-lives extend to weeks, months and even years, depending on whether they reside in water, soil or sediment. Unless chemical production is being reduced, we will continue to detect these compounds in the environment as well as in food and breast milk.
OC&PA: What did the FDA panel conclude?
RH: Concentrating on product efficacy, the panel concluded that use of antimicrobial personal care products offers no benefit over use of regular soap and water, based on the available science. Studies conducted to date were either inconclusive or not properly designed to show a true benefit from these products.
OC&PA: Do antimicrobial products have a purpose beyond consumer use, say for a hospital or other health care setting?
RH: Certain populations in health care settings may benefit from using antimicrobials. However, this benefit does not necessarily translate to the population at large. The annual use of antimicrobials in health care settings is miniscule compared to the millions of pounds of persistent biocides contained in personal care products used and dispersed into the environment today. The FDA panel concluded that the abundance of antimicrobial consumer products in everyday life lacks a scientific foundation. It may be more of a marketing phenomenon.
OC&PA: What about alcohol-based hand sanitizers?
RH: Hand sanitizers are designed for use without water. They are often alcohol-based and never contain persistent antimicrobials such as triclosan and triclocarban. Their active ingredients can kill germs but do not appear to contribute to antibiotic resistance. Several members of the FDA panel indicated that these products may be useful in situations where hand washing is desirable but impractical.
OC&PA: Is there anything you would like to add?
RH: We as consumers buy antimicrobial products to stay healthy. In our desire for protection from potentially harmful germs, we often fail to consider the risks inherent in both the chemical exposure we voluntarily subject ourselves to and the potential increase in antibiotic-resistant pathogens in our household, workplace and the environment. In the absence of a known benefit, it is difficult to justify taking any additional risks. Regular soap and water have worked for centuries and there is no scientific evidence that this winning combination will lose its punch anytime soon.--Tim Parsonspaffairs@jhsph.edu.