Dimples are a widely recognized facial feature, creating small indentations that usually become visible when a person smiles. Their presence and visibility are tied to facial anatomy, genetic inheritance, and changes in the distribution of facial fat over time. Understanding the science behind dimples clarifies why they may appear, disappear, or become more pronounced as a child grows.
The Anatomy Behind Dimples
Cheek dimples result from an anatomical variation in the Zygomaticus major muscle. This muscle is responsible for pulling the corners of the mouth upward during a smile. In people with dimples, the muscle often exhibits a bifid or double-headed structure, meaning it is split into two distinct bundles.
One muscle bundle inserts at the corner of the mouth, while the other attaches directly to the overlying skin. This dermal tethering means that when the muscle contracts, the skin is pulled inward, forming the depression. This variation explains why dimples typically only appear dynamically with facial movement. Chin dimples, also known as a cleft chin, are formed differently, resulting from an incomplete fusion of the lower jawbone during fetal development.
The Genetics of Dimple Inheritance
Dimples are generally considered to be an inherited trait, often described in traditional models as an autosomal dominant characteristic. This means a child would only need to inherit the genetic variation from one parent to have a high probability of developing the trait. However, the actual inheritance pattern is now understood to be more complex and is likely polygenic, involving the influence of multiple genes.
This complexity explains why the trait does not always follow the straightforward rules of Mendelian inheritance. A child may still develop dimples even if neither parent has them, or conversely, a child may not have them despite both parents possessing the trait. Recent genetic studies confirm that multiple genetic variants contribute to the final expression of the feature. The presence of dimples is highly heritable, but the precise mechanism of expression can be unpredictable.
When Dimples Appear and Change
The timeline for when dimples appear in babies is highly variable. Some infants are born with dimples that are visible right away, especially when they make facial expressions like crying or smiling. In other cases, the dimples may not become apparent until later in infancy or early childhood.
The visibility of dimples is heavily influenced by buccal fat pads, or “baby fat.” Newborns have significant fat in their cheeks, and indentations seen early on are often transient, caused by fat pressing on the underlying muscle structure. These temporary indentations may disappear as the baby grows and loses their rounded facial appearance, often fading away as they transition from infancy to toddlerhood.
Genetically-linked dimples typically become more consistently visible as the child’s face matures and the baby fat diminishes, generally between six months and two years of age. If the bifid Zygomaticus major muscle is present, the dimple becomes more defined once facial fat is reduced. Dimples may last a lifetime, or they may disappear completely by adolescence or young adulthood as the muscles fully grow and facial structure changes.