Handwashing Effectiveness Not Affected By Water Temperature

MedicalResearch.com Interview with:

Donald Schaffner, PhD Extension Specialist in Food Science and Distinguished Professor Rutgers-New Brunswick

Dr. Schaffner

Donald Schaffner, PhD
Extension Specialist in Food Science and Distinguished Professor
Rutgers-New Brunswick

MedicalResearch.com: What is the background for this study?

Response: We been interested in handwashing and cross-contamination research for more than 15 years. About 10 years after I started as a faculty member I was approached about doing research in this area. The first paper republished has turned into my most highly cited paper. I think it was mostly a matter of being in the right place at the right time, with the right idea.

This latest bit of research came out of my ongoing participation in the Conference for Food Protection. This is an unusual meeting, and unlike any other scientific conference. It’s a group of industry scientists, government regulators, and academics would get together every two years to help the FDA Center for Food Safety and Applied Nutrition update a document called the Model Food Code. The code has no regulatory standing, but it is used by state health agencies as the basis for state food codes that regulate restaurants, supermarkets, and other food service establishments.

There are several provisions in the code that we wanted to try to impact with our research. The code currently states that hands must be washed in warm water. The plumbing section of the code also states that hand wash sinks must be capable of dispensing water at 100°F. We wanted to explore whether there was any scientific basis statements.

In some recent survey-based research, graduate student that is also the first author on this manuscript surveyed the Internet for the kind of advice was offered on handwashing posters that provide advice on how to wash your hands. He found that the recommendations varied widely including recommendations on how long to wash your hands.

MedicalResearch.com: What are the main findings?

Response: The first finding is that water temperature did not make any difference. We studied 60, 80, and 100°F. And no matter what temperature was used, there was no difference in the number of bacteria removed during the hand wash.

The second finding was regarding lather time. We defined lather time is the time from when the soap was added to the hands, until rinsing of the soap commenced. We studied for lather times: five, 10, 20 and 40 seconds. We saw a statistically significant difference between five and 20 second lather times, so my recommendation is to use at least a lather time of 10 seconds.

We also studied three volumes of soap: 0.5, one and two mL. We did not see any difference in effectiveness between the three volumes. I do want to point out that this does not mean people should use less than 0.5 mL, or that they don’t need to use soap at all.

Finally, we compared antibacterial and non-antibacterial soaps for all of the treatments. We saw a small (0.3 log, or 50%) but highly statistically significant (p = 0.0003) difference between bacterial and non-antibacterial soap. This is consistent with the difference we’ve seen in our analysis of the literature, as well as other research we’ve done with antibacterial soap. We have also published a computer simulation paper showing that even a small difference like this can lead to a significant reduction in foodborne disease.

MedicalResearch.com: What should readers take away from your report?

Response: I think one of the key take-home messages is that handwashing is important, and that it’s better to wash your hands than not. That said, the person-to-person differences are often much larger than the differences between variables like lather time or soap volume.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

Response: Clearly there is much more research to be done in the field of handwashing. One of the variables did not use in this study, but which we have investigated in the past, as have others, is the presence of debris on the hands. We know that hands that are visibly clean, but inoculated with bacteria may behave differently than hands that contain food debris, soil, or feces, as well as microorganisms. We also know that viral diseases can be spread by hands, and that bacteria and viruses on the hands may react differently to a hand wash.

MedicalResearch.com: Is there anything else you would like to add?

Response: It’s been very interesting and exciting to do this kind of research. One common question we get askwd about this research is whether we received industry funding. While we have received funding in the past from the soap and detergent industry, we did not receive industry funding for this research. Several of our co-authors on this work do work for GOJO Inc., a company that sells soap and alcohol-based hand sanitizer. They donated all the soap we used in this work, but more importantly they helped us think through our experimental design, and the factors that were really important. I think it is vitally important when doing the sort of research to at least talk with folks in the industry. There is truly an art and a science to properly formulating soap. Much of the knowledge on how to formulate an effective soap is not in the peer-reviewed literature, and does require industry involvement. While I’m sensitive to claims about conflict of interest, I stand by all my work no matter how it’s funded.

MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.


Dane A. Jensen, David R. Macinga, David J. Shumaker, Roberto Bellino, James W. Arbogast, Donald W. Schaffner. Quantifying the Effects of Water Temperature, Soap Volume, Lather Time, and Antimicrobial Soap as Variables in the Removal of Escherichia coli ATCC 11229 from Hands. Journal of Food Protection, 2017; 80 (6): 1022 DOI: 10.4315/0362-028X.JFP-16-370

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Last Updated on June 5, 2017 by Marie Benz MD FAAD