A: If there was a sign encouraging them to do so.

Here’s a tip: After you shake hands with someone, go wash your hands. And use plenty of soap! Only 5 percent of people properly wash their hands after using the toilet in a public restroom. That means an astounding 95 percent do not, according to a study by MichiganStateUniversity researchers. The study: A dozen research assistants were specially trained to hang out in public restrooms and unobtrusively watch people’s behavior. The following information was recorded on 3,749 men and women who visited the restrooms:

• Did they leave the restroom without washing their hands?
• Did they just wet their hands without using soap?
• Did they wash their hands with soap?
• How long did they keep their hands under running water?

The results:

• 33 percent did not use soap.
• 10 percent didn’t wash their hands at all. Broken down by gender: 15 percent of men and 7 percent of women skipped the sink.
• When they did wash their hands, fully half of men did not use soap, compared with 78 percent of women who did use soap.
• While women wash their hands better than men, most are not doing it correctly.
• Only 5 percent washed their hands long enough to kill illness-causing bacteria.
• People were less likely to wash their hands if the sink was dirty.
• People were more likely to wash their hands if there was a sign encouraging them to do so.
• It takes 15 to 20 seconds of hand washing to kill disease-causing germs, but most people only wash their hands for about 6 seconds, including restaurant workers. Improper hand washing contributes to nearly 50 percent of all foodborne illness outbreaks.