Smiling can bring you health benefits even if you don’t start out feeling happy. So, next time you’re so frustrated you feel like gritting your teeth, try grinning instead.
University of Kansas researchers conducted a study to test the saying “Grin and Bear it.” The research, published in the Journal of Psychological Science, was to determine how a smile affects the rest of the body once it’s in place.
The Experiment
Subjects performed a couple of different stressful tasks, including tracing the outline of a star using the non-dominant hand while looking in a mirror (phew!) and plunging a hand into a bowl of ice water for one minute.
These tasks were done one of the following ways: without smiling, with the teeth held in a moderate smile, and with a broad smile. A broad smile engages not just muscles around the mouth, but the eyes as well. These subjects practiced how to engage those muscles, though not asked explicitly to smile.
Everyone held a chopstick between their teeth to provide a means of standardizing the facial expressions. The chopstick provided a method of standardizing the facial expressions, to compare them, and to create a smile artificially.
Following the exercises, stress levels were taken two ways: They took heart rate measurements and asked the subjects how stressed they felt while doing the tasks. 
All of the subjects, regardless of the smile type, felt the same degree of stress while doing the tasks. What differed was how fast the various groups’ heart rates returned to normal. The heart rates of the participants with no smile took the longest to recover. The subjects with a broad smile recovered the quickest.
Fake It Till You Make It?
If you “put on a happy face” would you feel less stressed? It depends. Another study in 2007, published in the Journal of Occupational Health Psychology, encouraged subjects to be enthusiastic and to hide frustration. These participants were exhausted and tended to make more mistakes. The energy was lost and felt by workers trying to act happy on the surface when they are not.
However, researchers write that focusing on positive thoughts or reappraising a troublesome situation can help improve feelings over time.
“Smiling is not a cure-all for every type of stress, especially for long-term stressors,” she says, like repeatedly dealing with hostile customers or other difficult people. Still, it may offer relief for the brief, acute stressors, if only for a short time,
So next time you’re stuck in a boring meeting, caught in traffic, or doing a dreaded task, consider smiling. You may feel better and bring your heart rate down, also.