The smile is a type of facial expression that results from a feeling of joy, happiness, or any feeling of satisfaction that the human being presents. From the anatomical-physiological point of view, it can be mentioned as a smile the product of the total contraction of 17 muscles of the face close to the oral and orbital cavity (eyes), in humans it is mostly produced when there is a satisfactory or pleasant feeling, without However, it can also be evidenced in states of anxiety, anger or sarcasm, being on these occasions an involuntary contraction.

Specialized studies have shown that the smile is not a voluntary or learned movement, being this purely innate (proper from birth), this explains why people who are blind from birth know how to smile, however, the facial silhouette called smile is only of human use, on the contrary, when animals make a grimace similar to a smile, it is not due to a feeling of satisfaction, but rather occurs spontaneously due to situations of threat to the animal.

As time goes by, the smile movement can be applied for different occasions, to show gratitude, to greet acquaintances, also as a sign of kindness, etc. Several scientists have described different types of smiles: in the first place we can mention the “Duchene” smile, this is produced involuntarily by the human, it exerts the contraction of the facial muscles such as the zygomatic muscles, and the muscles near the the eyes, known as a genuine smile; “professional” smile, this is the smile applied to show cordiality towards people who are in a common room; finally you can mention the smile “sardonic” this is a type of involuntary contraction caused by contamination with a pathogen called clostridium tetani, this is responsible for the pathology known as tetanus, which is characterized by producing a contraction of the muscles of the back, neck and face, making it impossible for the patients to achieve closure of the mouth.

Smiling not only modifies the contraction of muscles, thus changing a person’s facial expressions, but also induces an endocrinological change, when smiling in the diencephalon (area between the brain and brainstem) a hormone called endorphins is secreted , which generates the feeling of well-being or pleasure, reducing emotional or physical pain that the individual presents.