Good science is fucking hard: Handwashing sensation finds cool water as effective as hot water for removing germs

I didn’t know Don Schaffner, food safety guru and pop sensation at Rutgers University, was a Brittney Spears fan.

But he writes, whoops, I did it again, putting publication of peer-reviewed research ahead of press release.

We had an article published in the Journal Food of Protection earlier this week. While this current research is no five second rule, I thought it might garner some press interest, so I worked with colleagues at my university to put together a press release. I do enjoy talking to the media as part of my job, and it’s especially fun when it’s my own research.

(That’s why I became a professor, because I was bored talking about other people’s research and wanted to talk about my own — dp)

I thought I would take a little bit of time and share with readers about the process, because you folks are into this too.

An early draft of the press release had the title “Cool Water as Effective as Hot for Killing Germs”. This led to a conversation with my colleague in media relations who explained that using the word “killing” in the headline would lead to many more hits on Google (the modern-day equivalent of “if it bleeds, it leads”). I had to explain, that while I know all about search engine optimization (SEO), I could not in good conscience tell a scientific fib. Handwashing, for the most part does not kill germs, it simply removes them from your hands, and allows them to be washed down the drain.

Which brings me to antibacterial soaps – which seem to kill germs. This particular research article did look at the question of antibacterial soaps, and basically led to the same conclusion as our other on the issue: antibacterial soaps do work better than plain soaps when it comes to reducing bacterial counts on the hands, probably because there is some actual bacterial killing going on. For a variety of reasons, antibacterial soaps tend to work people up into a lather (pun intended… who says scientists have to be serious?). I had one journalist tell me [no link for you, sleazy British Tabloid] that they had already come to the conclusion that antibacterial soaps don’t work, and could I just say that. No, I explained I could not just say that, because that’s not what our research found. Instead, we found a highly significant difference (p= 0.0003) between hand washes with an antibacterial soap, and with a similarly formulated plain soap.  In this particular study the difference was small, about 0.3 log. I know many readers of this blog are comfortable and thinking on the log scale,  but for you non-microbiologists, 0.3 log corresponds to about a 50% greater reduction. Now 50% sounds like a lot to a non-microbiologist, but when you’re doing food microbiology, sometimes the data themselves can vary by 0.5 logs, or almost 70%.  So what we ended up saying in the manuscript was,  while highly significant, the difference was “within the range of error for microbiological data (i.e., a clinically insignificant difference).” I wish I’d said that a bit more forcefully in the manuscript, but sometimes we have to make compromises in peer review. The bottom line? I believe that antibacterial soap works better than plain soap in reducing bacteria on your hands. We reach this conclusion in our meta-analysis on the subject, and even this relatively small difference can have a profound effect on public health, at least if you believe our risk assessment manuscript on the subject.

I wanted to stress in the press release, and what I’ve been leading with during my media interviews, is that wash water temperature makes no difference, at least in the range that we studied (~ 60°F to 100°F). Our data show that there was no significant difference, no matter what temperature was used in the hand wash. Water temperature has along an interesting history in the FDA model food code. It used to be that the code specified a specific water temperature for washing the hands. It turns out that that temperature was based on the temperature at which bacon grease liquefies. The current code says that hands must be washed in warm water. Elsewhere in the current code it specifies that a hand wash sink must be capable of dispensing water at 100°F,  hence our reason for doing the research.  One point that I’ve been stressing in the media interviews is that it’s all about comfort. We want people to be comfortable when their washing their hands, and so my advice is use whatever water is most comfortable for you. It remains to be seen whether we will be able to change what’s in the code. Check back in 2018 after the next Conference for Food Protection

We looked at several other factors in this research as well. We investigated the volume of soap used: 0.5 mL, one mL and two mL, and we found no difference between these volumes of soap. Of course this doesn’t mean you can use as little soap as you want, my recommendation is to use at least 0.5 mL. Using more than this doesn’t seem to make a difference. This is also consistent with what we found in our [meta-analysis](

In a recent paper published in Food Protection Trends, my PhD student Dane Jensen (who was also the lead author on this handwashing study), and I published an analysis of recommendations on handwashing signs.  Dane had a hand (pun intended, see above) in several of the handwashing research manuscripts coming out of my lab in recent years. What we found in the FPT handwashing signage research was that handwashing recommendations were all over the place. So we decided to study lather time in this current manuscript. For purposes of our research we defined lather time as the time from when the soap is applied, until the water rinse begins.  We studied five, 10, 20, and 40 second lather times.  We only saw a statistically significant difference between lather times of five and 20 seconds.  The recommendation I would draw from this finding, is to lather for at least 10 seconds.  Lathering for more than 10 seconds does not appear to offer any additional benefit.

 One of the questions that seems to come up again and again in media interviews on this topic is “who funded the research”. While I understand the motivation for the question, it’s starting to get under my skin (okay okay, I’ll stop with the puns). The question seems to imply that somehow if I take money from the industry, my results are not to be trusted. I strongly resent the implication. It’s damn difficult to get grants these days, and I don’t think it’s going to get any easier until something  changes in Washington. We funded this research using discretionary money, but I’m proud that we did it in collaboration with our co-authors from GOJO.  They were instrumental in helping us think about our experimental design, plus they gave us free soap. They are also really smart and hard-working scientists, who really sweat the details.

Is this the last word on handwashing? I doubt it. We’ve got at least one more paper from Dane’s dissertation in the pipeline, and I’ve still got more ideas. If anyone reading this believes that industry funded research is somehow tainted, and you’ve got $250,000, please get in touch.

That’s the background and shows just how much good scientists sweat the details, whereas any hack can make a claim, spread it on the Internet, supported by no data, just interpretation.

I’ve got a modest 70 peer-reviewed papers, book chapters and a book, but when I had a big lab with the money flowing, I got bored. That’s just me.

Surprisingly I still get cited in peer-reviewed journals a few times a week, so I know I’ve got a body of work that people go to.

Thee scandals of pay-for-publication journals are a smear on the scientific community, but until someone comes up with a better system, peer-review largely works.

I’ve kept my mouth shut for years while papers got written, reviewed and published.

No PR before publication.

Those who do are attention-seeking assholes and another smear on the profession.

Here’s an edited version of the Rutgers PR.

Washing our hands can keep us from spreading germs and getting sick. But a new Rutgers-New Brunswick study found that cool water removes the same amount of harmful bacteria as hot.

“People need to feel comfortable when they are washing their hands but as far as effectiveness, this study shows us that the temperature of the water used didn’t matter,” said Donald Schaffner, distinguished professor and extension specialist in food science.

In the Rutgers study, published in the June issue of the Journal of Food Protection, high levels of a harmless bacteria were put on the hands of 21 participants multiple times over a six-month period before they were asked to wash their hands in 60-degree, 79-degree or 100-degree water temperatures using 0.5 ml, 1 ml or 2 ml volumes of soap.

“This study may have significant implications towards water energy, since using cold water saves more energy than warm or hot water,” said Schaffner. “Also we learned even washing for 10 seconds significantly removed bacteria from the hands.”

While the study indicates that there is no difference between the amount of soap used, more work needs to be done to understand exactly how much and what type of soap is needed to remove harmful microbes from hands, said co-author Jim Arbogast, vice president of Hygiene Sciences and Public Health Advancements for GOJO. “This is important because the biggest public health need is to increase handwashing or hand sanitizing by foodservice workers and the public before eating, preparing food and after using the restroom,” Arbogast said.

These findings are significant, particularly to the restaurant and food industry, because the U.S. Food and Drug Administration issues guidelines, every four years, to states. Those guidelines currently recommend that plumbing systems at food establishments and restaurants deliver water at 100 degrees Fahrenheit for handwashing.

Schaffner said the issue of water temperature has been debated for a number of years without enough science to back-up any recommendation to change the policy guidelines or provide proof that water temperature makes a difference in hand hygiene. Many states, in fact, interpret the FDA guidelines as a requirement that water temperature for handwashing must be 100 degrees, he said.

The FDA is scheduled to hold a conference in 2018 to discuss the existing code and any modifications that should be made and Schaffner would like to see the water temperature policy revised at that time.

“I think this study indicates that there should be a policy change,” said Schaffner. “Instead of having a temperature requirement, the policy should only say that comfortable or warm water needs to be delivered. We are wasting energy to heat water to a level that is not necessary.”

Antibacterial soaps can reduce risk of foodborne illness

Friend of the blog Don Schaffner has published some new research that shows  the use of antibacterial soaps can reduce the spread of harmful bacteria – that often leads to foodborne illness – more effectively than using non-antibacterial soaps.

The research, published in the peer-reviewed Journal of Food Protection (Vol. 77, No. 4, 2014, pp. 574-582), used new laboratory data, together with simulation techniques, to compare the ability of non-antibacterial and antibacterial products to reduce the risk of the infectious disease shigellosis, which is often spread during food preparation.

antibacterial.soapLead researcher Donald Schaffner of Rutgers University’s Department of Food Science says the data show that the use of three antibacterial wash products result in a statistically significant reduction in the presence of Shigella (the bacterium that causes shigellosis) compared to the use of the non-antibacterial soaps.

“This exciting research blends quantitative microbial risk assessments with an impressive set of laboratory data to show that antibacterial treatments are more effective than non-antibacterial treatments in reducing disease,” said Dr. Schaffner.

In the study, 163 subjects were used to compare two non-antibacterial products and three antibacterial products, with a study design intended to simulate food handling. The participants’ hands were exposed to Shigella and then treated with one of the five products before handling food melon balls. The resulting levels of Shigella on the food were then measured.

The levels of Shigella were then used to predict the outcome from an event in which 100 people would be exposed to Shigella from melon balls that had been handled by food workers with Shigella on their hands.

The data show all three antibacterial treatments significantly lowered the concentration of Shigella compared to the non-antibacterial treatments. Based on this model, the paper predicted that by washing with the antibacterial treatments, the number of illnesses could be reduced tenfold.

“This research provides strong evidence that antibacterial soaps are significantly more effective than non-antibacterial soaps in reducing Shigella on the hands and its subsequent transfer to ready-to-eat foods,” the authors write.

The American Cleaning Institute ( and the Personal Care Products Council ( provided funding for the research as part of the groups’ ongoing commitment to product and scientific stewardship to affirm the safety and benefits of these products.

An abstract summarizing the paper, “Quantitative Microbial Risk Assessment of Antibacterial Hand Hygiene Products on Risk of Shigellosis,” can be found online at