One of the best ways to prevent the spread of infection in hospitals is to make sure doctors and nurses wash their hands. But studies have shown that health-care professionals sometimes wash as little as half as often as they should.

Hospitals have tried several ways to increase hand-washing: hiring observers to note who is washing and when, setting up video surveillance, even, like Jefferson University Hospital, making a promotional music video.

After spending time at the hospital for the birth of his first daughter, Wharton School management professor and organizational psychologist Adam Grant decided to attack the problem from a psychological angle.

“People have a very hard time believing health messages when they talk about your own health,” Grant said.

Especially, he hypothesized, if you are around germs all the time, like doctors are, and rarely get sick.

“But if you give people the exact same info and tell them someone else they know is at risk, they’re much more likely to find it believable and plausible,” Grant said.

In an experiment, Grant tested how often doctors and nurses used hand sanitizer when two different signs were posted by the dispensers. 

“Hand hygiene prevents you from catching diseases,” said one. 

"Hand hygiene prevents patients from catching diseases,” said the other.

Grant found that health-care workers were almost 10 percent more likely to sanitize when the signs emphasized vulnerable patients, and used a third more gel.

The study lasted only two weeks, though, so it is hard to know if the effect would last once the novelty of the signs wears off.

The study will be published in an upcoming issue of the journal Psychological Science.