Last week, the U.S. Food and Drug Administration (FDA) effectively banned a personal hygiene product used by millions of Americans. Because manufacturers failed to demonstrate that 19 chemicals used in antibacterial soaps are safe and more effective than regular soap in preventing illness and the spread of infections, companies will have a year to remove the ingredients from their products.

Of those chemicals, the most commonly found in liquid antibacterial soap is triclosan, and the most common in bar soap is triclocarban. These compounds have been found to disrupt development of the reproductive system and metabolism in animals, and may contribute to making bacteria resistant to antibiotics.

In bringing attention to antibacterial soap, the FDA cited a study led by Stanford epidemiologist Stephen Luby showing no significant difference in results from plain soap and antibacterial soap. To better understand the issues around antibacterial soap, we spoke with Luby, a professor with the Stanford School of Medicine and a senior fellow with the Stanford Woods Institute for the Environment and the Freeman Spogli Institute for International Studies.

How did your 2005 study in Pakistan shed light on the question of antibacterial soap’s efficacy? 

That study compared the health outcomes from antibacterial soap and soap that was indistinguishable from and otherwise chemically identical to the antibacterial soap, but without triclocarban. Compared with a control group who received school supplies, children living in households who received soap and handwashing promotion had 52 percent less diarrhea, 50 percent less pneumonia and 45 percent less impetigo. Impetigo, a skin infection, was a particularly important outcome, because laboratory studies had suggested that triclocarban would have antibacterial activity against the organisms that most commonly caused impetigo. There was, however, no difference in any of the health outcomes between children living in households who received the plain soap compared with children who received the antibacterial soap.

The study was influential, because its blinded design and large size provided a rigorous test of the hypothesis of the health benefit of antibacterial soap. The finding that there was a major benefit to handwashing was an important outcome and demonstrated that people were using the soap fine. Thus, the absence of any additional benefit with the antibacterial compound was a scientifically persuasive negative finding.

What’s to convince someone who argues that we don't know whether chemicals in antibacterial soap have any harmful effects on humans?

I consider animal studies to be important indicators of impact on biological organisms. We are biological organisms, so if we see adverse outcomes in animals, this is a concern.

In a 2013 interview with Popular Mechanics you said of triclocarbans, "I don't think that there is a huge negative effect associated with these compounds." Do you still feel this way?

I still agree with this notion. However, they are biologically active, and they have no proven efficacy. So, I don't see dumping tons of them into the environment each year as being a good idea. Why should we take the risk?

Generally, the burden for proving a chemical's safety has fallen on regulators in the U.S. In this case, it fell on manufacturers. Does this signal a change?

This was a very long process. The government's review of the data concluded that there was no compelling case for benefit. They argued that unless the manufacturers could present convincing evidence, that the ban would be instituted. Apparently whatever new evidence the companies may have presented, was not persuasive.

The FDA's new rule applies only to consumer hand washes and soaps. Other products, such as toothpaste, may still contain the chemicals if the manufacturer proves that the benefits outweigh the risks. What do you make of this uneven ban?

It seems that they focused a lot on evidence of benefit. Antibacterial soap has been carefully studied and not found to benefit health. Thus, there is no benefit to weigh against potential risk to health and the broader environment. I am not familiar with the toothpaste data, but, in general, I salute the FDA's use of good science on human health outcomes to inform their policy decisions.

What's your take on the potential harm from active ingredients under scrutiny in hand sanitizers and wipes (alcohol - ethanol or ethyl alcohol - isopropyl alcohol and benzalkonium chloride)?

I'd be surprised if there were big harms identified with these compounds, but it is prudent to assess them.

What should people do with the antibacterial soap sitting around their house?

I think it would be fine for people to use the rest of the antibacterial soap that is sitting around the house. That said, we can all be grateful that going forward neither they nor the environment needs to be exposed to these antibacterial compounds.