The facial feedback hypothesis states the idea that our facial expressions have an influence on our emotions, which affect both, others and ourselves; to the extent that without facial activation emotions could not occur.
The hypotheses regarding this subject, studied by several psychologists, date back to Charles Darwin (1872/1955) who believed that our facial expressions could enhance or inhibit the intensity of an emotion. If we smile, while we are sad, our expression of happiness will reduce our sadness.