Smile

A smile is a facial expression formed by flexing specific muscles. Most smiles involve the muscles located at the sides of the mouth.

Humans use these expressions to communicate many things. They can show delight, happiness, joy, or amusement. They also signal sociability. A smile is different from a grimace. A grimace is an expression of anxiety.

While smiles are common, they are not the same in every culture.

Researchers have identified two distinct types of smiles based on muscle use. The first is called a Duchenne smile. This type involves the zygomatic major muscle, which raises the corners of the mouth. It also involves the orbicularis oculi muscle. This second muscle raises the cheeks and creates lines around the eyes called crow's feet.

This is often called "smizing," or smiling with the eyes. The second type is a non-Duchenne smile. This involves only the zygomatic major muscle. Some call a polite, fake version a "Pan Am smile." This name comes from flight attendants at the former Pan American World Airways.

In the mid-19th century, a French neurologist named Guillaume Duchenne studied facial expressions. He discovered the physiological differences between these two types of smiles. Recent research has expanded on his work. Scientists now suggest that Duchenne smiles are uniquely associated with positive emotions. In contrast, a non-Duchenne smile might be used just to show politeness. Today, technology even helps analyze these expressions. Orthodontics uses artificial intelligence, such as software called Dynasmile, to assess Duchenne smiles in videos.

Smiling has a very long evolutionary history. Primatologist Signe Preuschoft traces the smile back over 30 million years. It likely began as a "fear grin" in monkeys and apes. These animals use barely clenched teeth to show they are harmless. They also use it to signal submission to dominant group members.

Other animals use mouth displays differently. For example, Barbary macaques use an open mouth to show playfulness. This may have similar roots to the human smile.

Cultural differences change how people perceive a smile. In the U.S. and France, smiling is very common. This is visible in photos of students or political leaders. However, smiles are less common in China or Japan. In some parts of Asia, people might smile to show embarrassment or emotional pain. In the former Soviet Union area, smiling at strangers can seem suspicious or even like a sign of stupidity. In some societies, too much smiling can suggest a person is shallow or dishonest.

Social settings also influence how smiles work. Smiling can be a way to make oneself more approachable or likable. It often acts as a pre-laughing device that paves the way to laughter. It can also be used as a response to someone else's laughter. However, smiling is not always positive. It can be used as a form of manipulation or reinforcement. In societies with high levels of corruption, people may trust smiling individuals less.

Some people have dimples that appear when they smile. Dimples are caused by a bifid zygomaticus major muscle. This means the muscle is split into two parts. One part inserts at the corner of the mouth. The other part inserts below the corner. These strands pull on the skin to create a dip. Dimples are a dominant trait, meaning they are genetically inherited. The shape of a person's face can change how they look. For example, people with long, narrow faces often have narrow dimples. People with short, broad faces may have circular dimples.