To figure out how water temperature affects hand sanitation, the researchers contaminated participants’ hands with harmless bacteria and then made them wash at 100, 80, and 60 degrees Fahrenheit. The researchers, who hailed from Rutgers University and Gojo Industries (a privately held manufacturer of sanitation products such as Purell) thought that 60 degrees was the coolest temperature that would be comfortable. The FDA, according to the study’s authors, requires that food service preparers (like restaurants) provide access to a sink capable of providing water that reaches at least 100 degrees. And historical surveys have found that most people are told to wash their hands in the warmest water they can tolerate. In general, people associate warmer water temperatures with cleaner hands. The study, however, didn’t find this to be true. Water temperature had no effect. That’s probably because the temperatures that we know kill bacteria (think boiling) are also likely to burn our flesh (ouch).