Most of us can spot a genuine smile. There’s just something different about it.

Well it was a French doctor in the 1860s who went to the trouble of stimulating facial muscles with electrical currents to discover just what reveals a genuine smile. It’s two muscles working together. The zygomatic major muscle that turns the corners of the lips up, and the orbicularis oculi muscle that squeezes the eyes into the famous fanned wrinkles also known as crows feet. Now it’s this latter muscle that’s involuntary, so the crows feet smile is considered the real spontaneous emotion and is known as the Duchenne smile.

It turns out the real thing has a lot of power. In this month’s Observer Magazine, Eric Jaffe outlines some fascinating effects of an honest smile. For instance a 30-year long study published in the Journal of Personality and Social Psychology found that women who displayed the Duchenne smile in their college yearbook photos had greater levels of well-being and marital satisfaction three decades later. Another study published this year in Psychological Science went further to make a connection between smiles and longevity. They found that professional baseball players who sported Duchenne smiles in their yearbook photo were only half as likely to die, in any given year, as those who had not.

So during this holiday season, when the cameras and cell phones come out, give it your best, most candid smile…it appears a good thing.

—Christie Nicholson