The research, led by a Michigan State University business scholar, suggests that customer-service workers who fake smile throughout the day worsen their mood and withdraw from work, affecting productivity.
But workers who smile as a result of cultivating positive thoughts - such as a tropical vacation or a child's recital - improve their mood and withdraw less.
"Employers may think that simply getting their employees to smile is good for the organization, but that's not necessarily the case," said Brent Scott, assistant professor of management.
"Smiling for the sake of smiling can lead to emotional exhaustion and withdrawal, and that's bad for the organization."
For the study, Scott and former MSU doctoral student Christopher Barnes studied a group of city bus drivers during a two-week period.
They examined the effects of surface acting, or fake smiling, and deep acting, or cultivating positive emotions by recalling pleasant memories or thinking about the current situation in a more favorable way.
The study is one of the first of its kind to examine emotional displays over a period of time while also delving into gender differences, Scott said.
The results were stronger for the women bus drivers, he said.
"Women were harmed more by surface acting, meaning their mood worsened even more than the men and they withdrew more from work," Scott said. "But they were helped more by deep acting, meaning their mood improved more and they withdrew less."
While the study didn't explore the reasons behind these differences, Scott said previous research suggests women are both expected to and do show greater emotional intensity and positive emotional expressiveness than men.
Thus, faking a smile while still feeling negative emotion conflicts with this cultural norm and may cause even more harmful feelings in women, he said, while changing internal feelings by deep acting would gel with the norm and may improve mood even more.
But while deep acting seemed to improve mood in the short-term, Scott said that finding comes with a caveat.
"There have been some suggestions that if you do this over a long period that you start to feel inauthentic," he said. "Yes, you're trying to cultivate positive emotions, but at the end of the day you may not feel like yourself anymore."
The study appears in the Feb issue of the Academy of Management Journal.