IStock Photo 8565000 © Aric Spence

“Employees must wash hands.” That’s what the sign says. Right there, over the sink in the bathroom.

So… if I’m not an employee, what are the odds I am going to wash my hands? It might depend on whether I’m a man or a woman. In an observational study, the odds a woman was observed washing her hands after using a public bathroom are 1 in 1.14 (88%). The odds a man was observed not washing his hands are 1 in 2.99.

It also could depend on whether I carry Mom’s voice in my head telling me I should. Common flu viruses can live 24-48 hours on nonporous surfaces like plastic light switches and metal doorknobs. Dr. Val Curtis of the Hygiene Center of the University of London found traces of feces on the hands of more than one in four British test subjects in 2008.

And location matters. Only 57% of men in a stadium bathroom in Atlanta were observed washing their hands. An even lower 53% washed up at two State Fairs and a car show in Minnesota. Women did better than men in Atlanta, but they had a lower rate of washing up in Minnesota.

Worldwide, handwashing can be a matter of life and death. A soap and handwashing promotion in Pakistan, for example, lowered the incidence of pneumonia by 50% in children under five, and of diarrhea by 53% in kids under 15. According to the Public-Private Partnership for Handwashing, ramping up of this simple practice could cut down significantly on the rate of child deaths from such causes.

Dr. Peter J. Pronovost, who leads the Quality and Research Safety Group at Johns Hopkins Hospital, told the New York Times in March, 2010 that doctors—that’s right, doctors—wash their hands just 30 to 40 percent of the time. The odds a person in a hospital will be diagnosed with a hospital-acquired infection are 1 in 22.06, and according to some studies, patients who acquire infections in the ICU suffer higher mortality rates than other patients. Implementing a hospital procedures checklist, which, among other measures, reminded doctors to always wash their hands, brought infection rates in the Johns Hopkins ICU down to nearly zero.

The US Centers for Disease Control and Prevention puts it simply. Its web page of instructions on how and when to wash your hands is headed flat-out: “Clean hands save lives!” But Mom could have told us that.