The Long-Lasting Effect of a Smile

Can smile have a long lasting effect on your life?

Posted Apr 18, 2011

Hi everyone! This is my first post and I would like to thank the editors of Psychology Today who invited me to write here. You can read a little bit about me in the bio page, but the short version is that I am a humorologist, a term coined by the anthropologist Mahadev Apte, one of the pioneers of modern humor research. Humorology is just like psychology or anthropology and all the other ologies in that it is so broad that it deserves to be its own discipline. What is unique about humor is that it attracts scholars from many different fields, not just the usual suspects within the humanities and social sciences. There are, for example, at least two books on the mathematics of humor!

This blog is my attempt to put together all the different facets of humor. I plan to write about the value of humor, smiling, and laughter, and their relationships with each other. My personal research focuses on the adaptive value of humor and laughter and the evolutionary forces that shape the way we use and perceive humor.


The first topic I want to cover is smiling. There is a debate over whether a smile is just a weak form of laughter--something of moderate intensity that happens when you hear a so-so joke--or if it has its own unique function, independent of laughter.

In other species, especially primates who are our closest relatives, there are two distinct expressions that are considered homologous to the human smile and laugh. Each one of them has a distinct facial display and appears in totally different situations. The silent bared teeth display is equivalent to the human smile, and appears to serve as an appeasing function or a sign of submission after a fight. The relaxed open mouth equates to human laughter and is more related to play behavior.  Both displays are found in numerous and distant primates and probably signify the evolutionary origin of human smiles and laughter.

In humans, however, we tend to generally distinguish between two types of smiles: the Duchenne and non-Duchenne smile (named after the French neurologist Duchenne de Boulogne who first studied them). The Duchenne smile is the genuine, honest, wholehearted smile. That's the one which really gives you pleasure. The non-Duchenne smile is the fake smile, the one people use to satisfy others but that doesn't give you the good feeling associated with a true smile. It is not always easy to distinguish between these two types of smiles but with some practice most people can identify each one of them.

The Duchenne smile, for example, involves the use of the muscles around your eyes. It is important to distinguish between the two smiles since only the Duchenne smile indicates enjoyment. As such it gives us a clue about the true state of the smiler's emotions.


Researchers in a recent study looked at hundreds of photos from one university's yearbook and recorded whether the students smiled or not, and if their smiles were genuine or fake. For the genuine smiles they also recorded the intensity of the smiles.

Later, they contacted the alumni and asked them about their relationship status: whether they were in a relationship, married or divorced. The alumni in this study graduated from the school anywhere between 1945 and 2005. The results showed that smile intensity predicted the divorce rate, meaning that the less intensely the students smiled, the more likely they were to divorce at some point in their lives. Of course, this is a correlation study and it does not mean that lack of smiling caused people to divorce. Nonetheless, the relationship between the two variables was impressive and it's remarkable to find a connection between these two seemingly unrelated variables after so many years.

These results were confirmed for another sample from the general population. Interestingly, in all samples women tended to smile more and with more intensity compared to men--a sex difference that is found in many other studies all over the world. This difference might have deep evolutionary roots (more on that in a future post).

It's not entirely clear why smile intensity is negatively related to divorce rate. If a smile is potentially an expression of a deeper personality disposition or temperament, it is possible that people who smile a lot have a more positive outlook on life or are happier in general--traits that might help them endure the bumps of a long-term relationship, or even choose good mates to begin with. All these interpretations are based on the assumption that people who smiled in the pictures, especially the ones with the more intense smiles, are also smiling more in general. I think it's probably true.

Another recent study looked at the relationship between smile intensity and longevity. This study used photographs of 196 baseball players taken from the 1952 Baseball Register. The use of known baseball players allowed researchers to control for many variables that could potentially affect longevity, such as year of birth, Body Mass Index (BMI), education, marital status, length of career and more. Forty six of the players were still alive at the time the researchers collected the data. For those who did die, several factors proved to be important for a long life, including college attendance, which reduced the risk of dying by 44 percent. More important, even after controlling for all other variables, smile intensity predicted longevity. Players who were pictured with Duchenne smiles were half as likely to die in any year compared to those who did not smile or those who had a fake smile. Moreover, smile intensity accounted for 35% of the explained variability in survival, an impressive number. Again, it is not clear why people who smiled genuinely lived longer, but it is possible that they are happier on average and hence reap the benefits of the positive emotion associated with smiles (sometimes referred to as mirth).

All these results are congruent with each other, highlighting the importance of a genuine smile. I personally find it very interesting that one snapshot of the face can potentially reveal so much about someone's behavior in the future. It is also interesting to note that while these studies involved people who presumably smiled voluntarily, in other studies where subjects are taught which muscles to move to produce the Duchenne smile, their brains show activities associated with subjective enjoyment. This may mean that we could force ourselves to smile genuinely and still enjoy the benefits associated with it.