Want to know the smile you received was true or fake? There is a simple test for it. True smile also known as Duchenne smile is smiling with both your mouth and eyes. It is a real and spontaneous smile if there is wrinkling at the corners of the eyes and a slight squint in them.
It is named after French neurologist Guillaume Duchenne who worked in mid-19th century on the physiology of facial expressions. As part of a series of experiments which involved stimulating the facial muscles of test subjects with electrical currents Duchenne discovered that two specific facial muscles have to work together in order to produce a genuine smile, namely: the zygomatic major muscle and the orbicularis oculi muscle.
He described 2 different types of smile. True smile or Duchenne smile reflecting a positive affect is due to contraction of zygomatic major muscle which raises the angle of mouth and the orbicularis oculi muscle causing the wrinkling around the eyes. Fake smile (Flight attendant smile or social smile) involves just the contraction of zygomatic major muscle which raises the angle of mouth.
Smile like other human expressions must be taken in context with the social situation. People posing for social media photos with their pouts and things are unlikely to be real. But after all said and done smile is the best accessory you can ever wear.