A smile comes naturally when we are feeling good. But what is the science behind this automatic expression of joy? How is smiling received in another person? How does it effect our physical health? How can it effect the wellbeing of others who weren't even directly exposed to it?
Research is exploring the answers to questions like these, leaving us with a much wider understanding of the complexities behind the smile.
Happy Baby, Happy Mom
Lane Strathearn, MD, from Texas Children's Hospital, examined how a smile can effect loved ones in a 2008 study published in Pediatrics exploring infants' smiles and their mothers' reactions.
In the study, 28 first-time mothers were placed in a functional magnetic resonance imaging scanner (MRI) to examine their brains' responses.
The mothers were shown images of both their own 5 to 10 month old infant, and an unknown child the same age. The images shown represented happy, sad and neutral facial expressions.
The MRI machine then measured the blood flow to different regions of the brain, showing where activity took place.
The results showed that when mothers saw the face of their own child, specifically if it was smiling, areas of the brain known to be associated with reward and the neurotransmitter dopamine were activated.
"These are areas that have been activated in other experiments associated with drug addiction. It may be that seeing your own baby's smiling face is like a 'natural high,' " said Dr. Strathern.
Areas involving emotional processing, cognition and motor and behavioral outputs were also activated, showing a complex response to their child's smile.
So a smiling baby may help a mother feel a "natural high." But what actions could a smile potentially illicit in others?
A 2003 study led by Nicolas Guéguen, PhD, from the Université de Bretagne-Sud in France, attempted to explain this subject.
This study, published in the journal Communication Reports, involved eight "confederates" (or knowing assistants in the study) and 800 randomly chosen passerby. The confederates consisted of four men and four women, aged 19-21, and the passerby were adults aged approximately between 20 and 50 years-old, who were in a supermarket in the West of France.
Researchers had the confederates smile at a passerby half of the time, a few seconds before another confederate dropped their computer disks, giving the passerby an opportunity to help.
Results showed that receiving a smile from a stranger increased participants' likelihood of helping another person later on.
After receiving a smile from the first confederate, 29.5 percent of the passerby helped the confederate with their dropped disks. Among those who did not receive a smile, 20.3 percent aided the second confederate.
The researchers found no significant differences based on the genders of either confederate, nor for the gender of the passerby alone.
However, some interaction in the relationship between the gender of the second confederate and the gender of the passerby was seen, in that males were more helpful to females and vice versa. (For example, male passerby helped female confederates 30 percent of the time and male confederates only 17 percent of the time, and female passerby helped male confederates 30 percent of the time and female confederates only 23 percent of the time.)
This study in particular shows a potential connection not only between a smiler and a receiver, but a father-reaching effect beyond these two direct participants.
According to the authors, this may be due to a positive effect that smiling has on mood, saying, "It is possible that the effect of smiling by the first confederate on the participant's helping behavior towards the second confederate is mediated by a positive mood activated by this nonverbal behavior."
Though this concept needs to be explored further, it presents an interesting idea of just how far out the effect of a smile can potentially ripple.
What's In It For Me?
In the previous studies discussed, one person's smile has helped others - be it through activating their reward center in the brain, or in making yet a further person more likely to receive help down the line. So what does a smile do internally for the smiler themselves?
A 2011 study published in Psychological Science, explored this subject. Lead author Tara Kraft, psychological scientist and MA candidate from the University of Kansas, examined the links between smiling and stress-recovery.
Kraft recruited 169 healthy college students for a study under the guise of "multitasking." The participants were first divided into three groups and trained to hold chopsticks in their mouths in a way that created a particular facial expression: either neutral, a standard smile or a Duchenne smile.
A standard smile uses only the muscles around the mouth, while a Duchenne smile also employs muscles around the eyes. This is sometimes known as a "genuine" smile.
Only half of both smiling groups were specifically instructed to smile. The others were unaware that this was the final goal, and only instructed in the muscle manipulation required to hold the chopstick.
After this training, the participants worked on holding the chopsticks as instructed while completing stressful multitasking activities that included putting their hands in ice water or tracing a reflection backwards in a mirror with their non-dominant hand.
Factors like heart rate, blood pressure and self-reported mood and stress levels were recorded at several points during testing.
Upon completion of testing, results showed that smiling participants in general, and Duchenne smilers in particular, had lower heart rates and stress levels after dealing with the stressor. Participants who were simply trained in the muscle movements and unaware that they were smiling also benefited compared to those with neutral expressions.
According to the authors, "Smiling showed widespread effects on cardiovascular recovery, with the smiling groups, regardless of awareness or type of smile, consistently returning closer to baseline levels of cardiovascular activity at the end of the recovery periods following both stress tasks."
Because of these findings, supervising PhD on the study, Sarah Pressman, suggested, "the next time you are stuck in traffic or are experiencing some other type of stress, you might try to hold your face in a smile for a moment. Not only will it help you 'grin and bear it' psychologically, but it might actually help your heart health as well."
More research needs to be done to fully understand the role that smiling plays, both in our own bodies, and in the bodies and minds of others. As research continues, the complicated and perhaps far-reaching effects of a smile are sure to be understood more and more.