In a new study, published in the Journal of Food Protection, scientists from Rutgers University-New Brunswick have found that when washing hands, the temperature of the water makes little to no impact on the number of remaining bacteria. Instead, the length of time spent washing is what counts. 

By asking 20 volunteers to wash their hands 20 times at varying temperatures - 15℃, 26℃, and 38℃ - as well as varying the amount of soap, researchers found that the amount of bacteria removed was no different. Prof. Donald Schaffner, one of the leading study authors, said “as far as effectiveness goes, this study shows us that the temperature of the water used did not matter.” Not only does the study claim that temperature does not matter, but also that the type of soap used is irrelevant. Regular soap is just as effective as antibacterial hand wash.  

Some critics have suggested that although the study is influential, the sample size used was too small, consisting of only 20 people, as well as only one, non-infectious form of bacteria tested. An NHS Choices article has called for investigations into “a wider range of products against other types of infectious organisms, such as viruses and fungi, as well as other strains of bacteria”, before any changes are made concerning regulations on handwashing technique.

The important take home message from this research is that increasing hand wash time from 20 seconds to 30 could significantly reduce any risks of food poisoning, infection, or spreading bacteria. 


Charlie Harington