PROBLEM: If you haven't consulted with the CDC's official guide to handwashing recently, you might be surprised to learn, as I was, that they don't distinguish between using warm or cold water. What is important, they say, is that you use soap, that you scrub well (including the backs of your hands, between your fingers, and under your nails) for at least 20 seconds, and that you dry your hands afterwards. The CDC also officially recommends humming the "Happy Birthday" song twice through for an accurate measure of time.
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METHODOLOGY: Since "research has established that people generally overstate the degree to which they wash their hands," researchers at Michigan State hid out in four different bathrooms to see what was really happening. More specifically, they deputized their research assistants to do so. The assistants, who were instructed not to draw attention to themselves (they entered data into their phones so it would look like they were just texting), categorized people as not washing their hands at all, as wetting their hands but not using soap, or as washing with soap. In addition, they timed how long each person spent scrubbing.
RESULTS: Of 3,749 people observed leaving the bathrooms, 66.9 percent used soap, while 10.3 percent didn't wash their hands at all. The other 23 percent of people stopped at wetting their hands, in what the researchers, for some reason, call "attempted washing" (as if maybe those people just weren't sure how to follow through). Although the researchers generously counted the combined time spent washing, rubbing, and rinsing, only 5.3 percent of people spent 15 seconds or longer doing so, thus fulfilling the requirements of proper handwashing. They average time spent was 6 seconds.