It's easy to tell if a smile is genuine: It's all in the eyes.

Image courtesy of Energy Star

Smiling doesn't seem like a particularly complicated act: You feel a happy emotion, the corners of your mouth turn up, your cheeks lift and your eyes crinkle. The overall effect tells the outside world that you're feeling happy on the inside. It's simple and, in most cases, totally spontaneous. We typically smile without making a concerted effort to do so.

In fact, most people are turned off by the appearance of a smile that takes effort, because so often it's obvious it's fake. It's not hard to detect a fake smile -- it usually involves only the mouth, not the eyes. The appearance of a genuine smile, one involving specific changes in the eyes in addition to the mouth (notably a crinkling of "crow's feet" and a downturn of the outer points of the eyes) is called a Duchenne smile, after the neurologist Guillaume Duchenne. Back in 1862 he identified the facial muscles involved in spontaneous smiling [source: Lienhard].

Awkward appearance aside, research performed over the past few decades suggests there could actually be a benefit to producing a fake smile. According to many experts, smiling may not only be an outward manifestation of a happy feeling. It may actually be able to cause a happy feeling. It's the exact opposite of how most people see the smile-happiness connection, but with a growing body of evidence supporting the effect, it seems there may be something to it.

But does that mean you can just turn off every bad feeling by faking a smile? Could you be a truly, permanently happy person if you master the look?

In this article, we'll look at the evidence for smiles causing happiness, see how significant the effect is and find out if there are other facial expressions that can trigger the emotions they're supposed to reflect.

In the 1970s and 1980s, quite a few psychologists got in on the smile-research action, with surprisingly consistent results.