Dimples, those charming indentations that appear on the cheeks during smiling, have long fascinated both scientists and laypeople alike.

Many find themselves wondering why these small face features often seem to run in families, appearing across multiple generations.

The Genetic Basis of Dimples

Dimples are widely regarded as a genetic trait, often associated with autosomal dominant inheritance. In simple terms, dominant traits require only one copy of the responsible gene to be present for the feature to manifest. This means if one parent carries the gene for dimples, there is roughly a 50% chance their child will also have dimples.

The gene responsible is thought to influence the structure of face muscles, resulting in the characteristic indentations.

Recent studies suggest that the genetic basis of dimples may not be governed by a single gene, but rather by complex interactions among multiple genes. This complexity can explain variations seen between family members, such as differences in dimple depth, unilateral versus bilateral dimples, or even why some children develop dimples later in life despite neither parent visibly having them.

How Dimples Form: The Role of Face Musculature

The appearance of dimples is caused by variations in the face musculature beneath the skin. Specifically, the zygomaticus major muscle—which controls smiling can have a variation where a split or a shorter muscle bundle tugs at the skin, creating a visible indentation. People without this muscular variation simply have a smoother muscle that does not pull the skin inward.

This muscular difference is what genetically predisposes individuals to have dimples, and its dominance means that this trait can be passed down and seen in successive family generations.

Penetrance and Variable Expression

While dimples often run in families, they do not always follow a straightforward hereditary pattern. This is due to phenomena called penetrance and variable expressivity. Penetrance refers to the likelihood that a person carrying a gene will actually express the related trait. In the case of dimples, some individuals may carry the gene but never develop visible dimples, effectively "skipping" a generation.

Variable expressivity means that even among those who do express dimples, the shape, size, or location may differ widely. One family member might have deep bilateral dimples, while another may possess a single, faint dimple on one cheek. These genetic subtleties result in the appearance of dimples being less predictable than other dominantly inherited traits, contributing to the diversity of the feature seen in families.

Spontaneous Mutations and Environmental Influence

Although dimples are predominantly genetic, spontaneous mutations can also result in the formation of dimples in individuals without a family history. These mutations alter the underlying muscle structure, causing an indentation to appear. Environmental factors do not directly cause dimples but may influence their visibility.

Why Dimples Persist in Families

Evolutionarily, dimples may have persisted and become common due to their association with positive social and aesthetic attributes. Their familial tendency is maintained because the gene variant responsible is dominant, allowing it to pass easily from one generation to the next.

Melanie Palm, M.D, a board-certified dermatologist and and cosmetic surgeon, states "Dimples are categorized as a unique face trait, which means there is really not a way to non-invasively or minimally invasively achieve this result."

Dimples are a genetically influenced trait primarily inherited through dominant gene transmission, involving variations in the face muscle structure. Their expression is shaped by complex genetic factors including penetrance and variable expressivity, which explain why dimples often run in families but with differing manifestations among relatives.