While conducting research on the physiology of facial expressions in the mid-19th century, Guillaume-Benjamin-Amand Duchenne (de Boulogne) identified two distinct types of smiles. The eponymous Duchenne smile involves contraction of both the zygomatic major muscle, which raises the corners of the mouth and the orbicularis oculi muscle, which raises the cheeks and forms crow's feet around the eyes.
A non-Duchenne, or politician smile involves only the zygomatic
major muscle. Research with adults initially indicated that joy was
indexed by generic smiling, involving just the raising of the lip
corners by the zygomatic major. More recent research suggests that
smiling in which the muscle around the eye contracts, raising the
cheeks high (Duchenne smiling), is uniquely associated with positive
There are also two types of laughter, Duchenne and non-Duchenne.
Duchenne laughter is the type of natural chuckle that people
experience when they see or hear something funny, which is often
contagious. This giggling involves the contractions of the
orbicularis oculi muscle and adds more pain relief than non-Duchenne
laughter, which is emotionless and context-driven. Duchenne laughter
might be so effective because it involves muscle activity much like
exercise, which releases endorphins. The capacity to sustain
laughter for periods of several minutes at a time may exaggerate the