The U.S. Food and Drug Administration released its decision Friday on banning 19 active ingredients in antibacterial soaps. The ruling, 40 years in the making, caps a decades-long debate over whether these germ-busting chemicals are safe and offer any advantage over ordinary soap. The ban includes the most widely used antiseptic in hand soaps, triclosan—after a large number of studies have fallen short of manufacturers’ claims about its health benefits.

“Consumers may think antibacterial washes are more effective at preventing the spread of germs, but we have no scientific evidence that they are any better than plain soap and water,” said Janet Woodcock, M.D., director of the FDA’s Center for Drug Evaluation and Research (CDER) in a statement. “In fact, some data suggests that antibacterial ingredients may do more harm than good over the long-term.”

When it hit the market in the 1960s, triclosan was intended for use in hospitals. But consumer demand for antibacterial soap surged due to increased marketing and media reports on dangerous infections. So manufacturers started making such soaps available to the public and added antibacterials to other products including toothpaste, mouthwash, toys, clothing and more. It was not long until concerns about the safety and efficacy of the triclosan-based soaps arose, however, and as soon as the FDA began regulating over-the-counter drugs in the mid-1970s, it proposed banning triclosan. Yet the ruling was never finalized and the decision fell by the wayside. It was not until 2010 that the FDA—after the nonprofit Natural Resources Defense Council sued it over the long delay—imposed a series of deadlines to determine the safety of antibacterial consumer soaps, hand sanitizers and health care soaps.

So what has four decades of research determined? Most studies have focused on triclosan, and as far as human health is concerned the research into its toxic effects has produced mixed results. For nearly every study that shows triclosan has some particular effect, another shows it does not. Yet one thing is clear: Several clinical studies, following several hundred households, have shown that triclosan-based soap does not prevent illness any better than regular soap and water alone.

There is also significant evidence that triclosan might worsen the problem of antibiotic resistance. Whereas plain soap and water simply dislodge bacteria from skin, triclosan weakens and kills the microorganisms. Until recently it was thought that triclosan acted indiscriminately—killing all bacteria in a number of ways—but now scientists know that it targets specific molecular pathways, acting more like an antibiotic. For example, triclosan homes in on an enzyme that plays a key role in bacterial metabolism—the same pathway that the tuberculosis-fighting antibiotic isoniazid targets. This similarity has raised concerns that bacteria could mutate and grow resistant to triclosan—and therefore also to the antibiotic. Allison Aiello, an epidemiologist at the University of North Carolina at Chapel Hill, notes that several studies have shown that bacteria can become resistant to triclosan in a laboratory setting. For instance, one study found that up to 7 percent of Listeria strains isolated from the environment and food products were resistant to chemicals found in antibacterial soaps.

There is no definitive research on whether triclosan adversely affects human health, but animal studies suggest that exposure to it and similar chemicals has the potential to disrupt hormones in the body, trigger allergies and be associated with some types of cancer. Whether those effects translate to humans is unknown; as some experts explain, animals in experiments are exposed to much higher doses than humans would ever experience. Still, because there is potential for harm the FDA is responsible for seriously considering possible health effects. “When there are conflicts in the data, it’s better to concentrate on costs than to not,” says Kristi Pullen, an environmental health scientist at the Natural Resources Defense Council. These effects are of particular concern because so many people use antibacterial soaps, and the chemicals they contain can be absorbed through the skin. According to a 2004 study, 75 percent of Americans have triclosan present in their urine.

Triclosan has been linked to environmental concerns as well. Once antibacterial soaps get washed down the drain, the chemicals they contain can persist in nature for decades . And their reach is far—triclosan has been found in lakes, streams, oceans and even house dust. “The large-scale use of triclosan-containing products has not brought any measurable public health benefits but instead resulted in environmental contamination of water, dust, soil and biota in countries around the world,” says Rolf Halden, an environmental engineer at Arizona State University in Tempe. In fact, scientists in Minnesota discovered in 2010 that when triclosan is treated at wastewater plants, it can be converted to dangerous dioxins. These chemicals, which are in the same family as PCBs and pesticides, persist for years in the environment and pose significant health threats to humans and animals. Triclosan-generated dioxins were found in lakes throughout Minnesota as well as the Mississippi River. As a result the state decided last year to ban triclosan; the restriction goes into effect January 1, 2017.

The FDA had several years to sift through stacks of studies and weigh the risks and benefits of antibacterial hand soap, and based its decision on whether to ban specific active ingredients on safety and efficacy grounds. “No drug is all good or all bad,” says Bruce Hammock, a toxicologist at the University of California, Davis. He notes that animal studies are difficult to translate to human use, and continues: “Everything is a benefit/risk equation.” Still, Hammock says, because triclosan and other chemicals in antibacterial soaps show no benefit over plain soap they should not be used by the general public. Sarah Reisman, an organic chemist at the California Institute of Technology, echoes these sentiments. She contends that there are not enough benefits to justify exposing masses of people to chemicals that may be harmful.

Paul DeLeo from the American Cleaning Institute, a business organization that supports the cleaning products industry, says companies have already been phasing out triclosan—largely due to the Minnesota ban. When interviewed last month, DeLeo thought the FDA would ban the chemical due to the state prohibition in Minnesota and consumer pressure. U.N.C.’s Aiello and Stuart Levy, director of the Center for Adaptation Genetics and Drug Resistance at Tufts University and a consultant on the FDA’s advisory committee, also thought the FDA would decide to put a national ban into effect.

Even though triclosan and the other chemicals on the FDA’s list are now outlawed, products probably will not be free of antibacterials anytime soon. DeLeo says companies have substituted triclosan with three other chemicals that are unapproved by the FDA: benzalkonium chloride, chloroxylenol and benzethonium chloride. These chemicals have been given an extension to remain on the market for at least another year while companies gather evidence supporting their safety and efficacy. Health officials worry these antibacterials will have the same problems as triclosan. “Replacing one with the other doesn’t seem like it will solve the problem,” Reisman says.