Why is it customary to shake hands only with the right hand? Legend has it that back before plumping and other sanitation inventions, the left hand was reserved for wiping ass and, therefore, never presented to another person in greeting or goodwill gestures. Although shaking with the right hand has stuck around, it’s too bad the left hand didn’t retain its designation, since a new study—published in this week’s Journal of Environmental Health—found 95 percent of people don’t properly wash after doing using the restroom.

A team of Michigan State University researchers collected hand-washing data by observing people in restrooms at bars, restaurants and other public places. Of 3,749 observations, only two thirds of people used soap when washing, and 10 percent failed to wash at all. Probably right before they shook someone’s hand.

Most astonishing, only 5 percent of people washed their hands according to the US Centers for Disease Control and Prevention guidelines. According to the CDC, hands should be washed vigorously with soap and water for 15 to 20 seconds—the length of time it takes to sing “Happy Birthday” twice. Michigan State students observed people wash their hands on average of just 6 seconds.

“These findings were surprising to us because past research suggested that proper hand washing is occurring at a much higher rate,” study researcher Carl Borchgrevink, a Michigan State associate professor of hospitality business, said in a statement.

Meanwhile, two different surveys show that 96 percent of people self-report consistently wash their hands. So are people liars or is there something weird going on at Michigan State? Maybe neither. Perhaps people wash their hands properly at home but can’t wait to escape the stench found in public restrooms. It could be since researchers found people were less likely to wash their hands later in the day and in the evening. Maybe they are in a rush to get back to their drinks with friends, or maybe the cleanliness of the restroom declined throughout the day.

Interestingly, guys were significantly less likely to wash properly than ladies. Michigan State students observed only half of men using soap and 15 percent didn’t wash at all, compared to 78 percent of women who used soap and just 7 percent who skipped washing altogether. Guys’ restrooms tend to be nastier than ladies’ rooms… it could be a pattern worth investigating…