"A smile is the expression of contentment and joy. When you feel happy, you smile. No other part of the body registers such a visible change. Research by Dr. Paul Ekman at the University of California School of Medicine in San Francisco has found that smiling registers in the part of the brain called the hypothalamus, where endorphins are produced and many hormones are regulated. Endorphins are naturally occurring opiates that relieve pain and give a sense of pleasure, peace, well-being, and even euphoria. According to Dr. Ekman's findings, smiles stimulate their production.
"Try a smile right now. Think of the love you offer, and smile. Hold that smile for about ten seconds. Every person that we've asked to do this has reported feeling better. In other words, not only do you smile when you feel happy, but you feel happy when your smile! Apparently you can't have one without the other. So if you want to experience a moment of happiness, smile. If you have a hard time smiling out of the blue, think of a close member of your family or another loved one, and remember the last time you saw him or her laughing. With this image, you will smile. This is joy traveling outward. Now, if you want your joy to go inward, configure your face into a smile. A moment of good feeling will follow."