A Biologist Explains Why Some People Have Smile Dimples

Smile dimples aren't a gift from a dominant gene—they're a quirk of muscle anatomy. A biologist explains that these cheek indentations result from a split in the zygomaticus major muscle, and the same phenomenon appears in two other surprising body parts.

The long-held belief that dimples are inherited as a simple dominant trait is a myth. In a recent article for Forbes, biologist Scott Travers breaks down the real cause: a variation in the facial muscle that creates a small gap. When a person smiles, the skin over this gap is pulled inward, forming the characteristic dimple. This muscle split is present at birth and remains stable throughout life.

This muscle anomaly is not unique to the cheeks. The exact same variant can produce a cleft chin—often called a 'butt chin'—where the mentalis muscle splits. Additionally, a similar split in the gluteus maximus muscle can create sacral dimples, commonly known as 'dimples of Venus.' All three features share the same developmental quirk: a divided muscle belly that tugs the overlying skin inward.

Travers notes that dimples are considered a minor congenital anomaly, but they are entirely harmless and often regarded as aesthetically pleasing. Studies estimate that about 20–30% of people have smile dimples, with some populations showing higher frequencies—for instance, up to 40% in certain East Asian groups.

The genetics, however, are more complex than once thought. Family studies show that dimples don't always follow a predictable inheritance pattern. Some children have dimples even when neither parent does, suggesting that multiple genes or environmental factors influence expression. The condition is not linked to any health problems.

This understanding challenges decades of oversimplified biology teaching. Textbooks have often used dimples as an example of a dominant trait, but the reality is that the muscle variation itself is rare as a systematic whole—each dimple variant arises independently. The insight shifts how we think about inherited physical features: not all are simple genetic switches.

Looking ahead, further research into the specific genetic markers controlling muscle development could reveal more about why these splits occur. For now, smile dimples remain a charming reminder that human anatomy is full of small, harmless variations. Whether on cheeks, chins, or lower backs, these quirks trace back to the same basic process: muscles that don't fully fuse during embryonic development.