Possessed by approximately 25% of the world’s population, dimples are a defect in the structure of the zygomatic muscle, which is responsible for smiling. In people with this physiological feature, a small bundle of the muscle gets attached to the bone. As a result, when a person smiles, a portion of the cheek is drawn inward. Dimples are particularly noticeable with chubby cheeks because fat makes the indentations more pronounced.