Plenty of soap and water

When my daughter was in primary school (we're doing University visits right now for her to start a biomedical undergraduate course, just to let you know how long ago that was), they did some tests in class with soap, antibacterial soap, some kind of indicator and an ultraviolet light. They wanted to see how quickly germs (bacteria, specifically) re-colonize one's skin after hand washing.

The bottom line was that warm soap and water worked as did the antibacterial soap containing the most widely used bactericidal agent, triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol), water alone wasn't very good at sloughing off bacteria though. But, under the UV lamp, the kids could see the regrowth of bacteria within a few seconds of hand washing. I don't remember whether they dried their hands with a communal towel after washing them, presumably they just let them air dry.

Now, those primary school findings from around a decade ago have been vindicated by scientists in Korea. In a paper just published in the Journal of Antimicrobial Chemotherapy [DOI: 10.1093/jac/dkv275], the team from the Department of Food Bioscience and Technology, at Korea University, Seoul, found no significant difference in bactericidal activity between plain soap and antibacterial soap (containing triclosan at the maximum allowed level in a domestic product, 0.3%) at a hand washing temperature of 40 Celsius or even 22 Celsius. The team artificially inoculated the skin of volunteer hand washers in their experiment with the microbe Serratia marcescens under laboratory conditions. S marcescens is a human pathogen associated with hospital-acquired infections, catheter-associated bacteremia, urinary tract infections and wound infections. The researchers also tested nineteen other bacterial strains cited by the US Food & Drug Administration (FDA) as potentially problematic.

Apparently, it took some 9 hours in the in vitro tests for triclosan to have a significant bactericidal effect. Now, I'm certainly an advocate of regular and frequent hand washing for the sake of disease control and kitchen hygiene, but 9 hours is a little too long for even my hand washing compulsion.

Min-Suk Rhee and colleagues explain how in late 2013, the FDA proposed a new ruling for manufacturers of personal cleaning products that those products must have demonstrable efficacy over conventional products, in other words antibacterial soap must be more effective than plain soap and water, otherwise it should not be on the market. The proposal emerged from growing concerns surrounding the emergence of increasingly intractable antibiotic resistance in pathogenic bacteria and how bactericidal soaps are apparently fostering an environment conducive to bacteria taking this undesirable evolutionary path.

"The present study provides practical information that may prove useful for both industry and governments," the team concludes. My personal conclusion is that, at least on this occasion, your grandparents knew best: wash your hands with plenty of soap and hot water and don't forget to wash behind your ears, you don't want potatoes growing there...

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".