I think everyone has heard the age old adage, “Don’t judge a book by its cover.” Sure it's a cliché, but it still provides a profound warning don't size up others based on their appearance.

And while this is definitely sound advice to guard us against clinging to prejudices and other judgmental behaviors, recent research has shown that our facial expressions — and our smiles in particular — may actually reveal a lot about us.

Curious about how yours measures up Read on for some of the fascinating scientific facts behind what your smile might mean ...

1. Your smile may predict your longevity.
In one study, researchers analyzed the smiles of baseball players in the 1952 baseball register and divided them into one of three categories (1) no smile, (2) a moderate smile, and (3) the “Duchenne smile.” (The Duchenne smile is that of genuine happiness the expression you make that crinkles up the corners of your eyes, elevates your cheeks, and raises the corners of your mouth.)

The results Turns out that the intensity of the players’ smiles was associated with longevity, and those who exhibited a partial smile lived longer than their more serious counterparts. Amazingly, those who had the widest smiles were likely to live longest.

2. Your smile may predict your overall health.
In another study, researchers focused their attention on select college yearbook pictures of female students, again looking for the tell-tale Duchenne smile as an indicator of genuine happiness.

The researchers then followed up with these women, 30 years after the pictures were taken and found that the women who'd had the genuine smiles reported higher life satisfaction and better health than the women whose smiles were not as bright.

3. Your smile may predict the strength of your romantic relationships.
In the same yearbook study noted above, the women who had the Duchenne smiles reported happier marriages than their peers. Another study that looked at the frequency of smiles in a collection of childhood and yearbook photos found that the individuals who smiled the least were five times more likely to be divorced in adulthood compared to those who smiled the most.

4. Smiling can indicate that you have a broader perspective.
A study that used facial electromyography (a device that measures muscle contractions in the face) found that individuals who smiled bigger, more often performed better on tasks that required attentional breadth and flexibility.

5. If you’re smiling before a fight, you could be in trouble.
While I’m assuming that most people on this site are lovers as opposed to fighters, this one is pretty fascinating. If you're about to engage in a combative situation (say, for example, a boxing match), a smile can signal weakness.

One study examined the face-off before the start of boxing matches and found that the fighters who showed the widest smiles were most likely to lose. Those who won by knockout smiled the least. So if you're in a competitive situation (especially one that involves physical domination), it might be in your best interests to display a more intimidating stance.

6. Putting on a smile could make you feel genuinely happier.

Various research studies have indicated that purposely putting on a smile can be an easy way to boost your mood. By activating your facial muscles into a smile, you feel a bit of a boost, and tend to report elevated mood.

But be wary, because you don't want to feel like you're forcing yourself to fake anything. While some people swear by fake-smiling as a strategy (and I’ve actually experienced the boost myself), there is some conflicting evidence.

BDST: 1719 HRS, JUNE 11, 2015
Edited by:  Sharmina Islam, Lifestyle Editor