Smiling could be good for your health.

Researchers are finding that wearing a smile brings certain benefits, like slowing down the heart and reducing stress. This may even happen when people aren't aware they are forming a smile, according to a recent study. The work follows research that established that the act of smiling can make you feel happier.

Some research suggests only a full and genuine smile affects the body in positive ways. Other studies, though, indicate even a polite smile may be beneficial. Frowning also may have a health effect: Preventing people from frowning, such as with the use of Botox, can help alleviate depression, a recent study found.

"You can influence mental health by what you do with your face, whether you smile more or frown less," says Eric Finzi, a dermatologic surgeon and co-author of the study on frowning.

A study published in the journal Psychological Science in November found that people who smiled after engaging in stress-inducing tasks showed a greater reduction in heart rate than people who maintained a neutral facial expression.

The study, which involved 170 participants, got people to smile unknowingly by making them hold a pair of chopsticks in three different ways in their mouth. One way forced people to maintain a neutral expression, another prompted a polite smile, and a third resulted in a full smile that uses the muscles around the mouth and the eyes.

"We saw a steeper decline in heart rate and a faster physiological stress recovery when they were smiling," even though the participants weren't aware they were making facial expressions, says Sarah Pressman, co-author of the study and an assistant psychology professor at University of California, Irvine.

Participants making a full smile performed better than the polite-smile group, but the difference wasn't statistically significant and needs to be studied further, she says.

"We smile because we feel not threatened," Pressman says. Over time that message evolved so the muscle activity involved in a smile sends a message to the brain signaling safety, which could translate into lower heart rate and stress levels.

Pressman is currently researching how smiling affects certain stress hormones, such as cortisol, and oxytocin, which is sometimes called the trust hormone. "We've already seen it with heart rate; we're hoping to see it with these other stress levels in the body," she says.

Click for more from the Wall Street Journal.