The smile face can be traced back to our ancestors, the primates, who still display a wide variety of facial expressions, including the grimace or fear grin and the submissive grin used to show "I am afraid." These expressions evolved into the human smile that now suggests that "I am harmless, friendly and happy to be with you." The smile is used all over the world to indicate pleasure and happiness. Even people who were born blind and have never seen a smile on others display a smile when they are happy and pleased.
A consciously formed smile produced only a weak feeling of happiness in laboratory-controlled experiments, but the opposite was produced by a frown. Even a forced frown produced a feeling of sadness. It is also evident that your smile will bring a smile to those you meet. Therefore, the smile is used to affect how others feel. When someone is sad, we often give them a big smile and tell them, "Don't cry, everything is going to be alright." And to some degree it helps!