Dimples are formed by muscle activity under the skin. Most muscles of human body are firmly attached to bones through tendon fibers, such as pectoral muscles and lower limb muscles.

Always like this. Facial expression muscles are an exception. It is directly attached to the facial skin. When the expression muscles contract, it affects the facial skin, so various wrinkles appear on the face, resulting in expressions of joy, anger, sadness and joy. The two dimples on the smiling face are facial skin and facial expression muscles, such as hamstring muscle and laughing muscle.

Not everyone will have dimples on his face when he smiles. Whether there are dimples is related to the development of expression muscles. People with less plump smiling muscles and less subcutaneous fat on their faces generally have no dimples when they smile.