A dimple is a small, natural depression in the skin, often associated with a youthful appearance or charm. While most commonly recognized on the face, these indentations are diverse and can appear in several locations across the body. The fundamental difference between the various types of dimples lies in their underlying anatomical cause, which ranges from variations in muscle structure to the tethering of skin by ligaments. Understanding the formation mechanism allows for a clear categorization of these features.
The Anatomical Basis of Facial Dimples
The most recognized dimples, those on the cheeks, are caused by a specific variation in the facial muscle called the Zygomaticus Major. This muscle is responsible for pulling the corners of the mouth upward when a person smiles. In individuals with cheek dimples, the Zygomaticus Major muscle is often bifid, meaning it splits into two distinct bundles.
The inferior bundle of this bifid muscle attaches to the dermis, the layer of skin beneath the epidermis. This attachment creates dermal tethering, tying the skin down to the underlying muscle tissue. When the person smiles, the muscle contracts and shortens, pulling the skin inward to create the characteristic depression.
This anatomical variation is considered a minor congenital defect, but it is common. The appearance of the dimple is entirely dependent on muscle movement, which is why these indentations only appear or deepen during facial expression.
Classifying Cheek and Chin Dimple Appearance
Cheek dimples are often classified based on their presentation, including whether they are unilateral (appearing on only one cheek) or bilateral (appearing on both sides of the face). Clinical studies suggest that unilateral dimples may be more common, though both forms are widely observed.
Classification also relates to the dimple’s location and visibility. For example, fovea buccalis describes a dimple located higher on the cheek, closer to the corner of the mouth. Cheek dimples are described as dynamic, meaning they are only visible when the face is in motion, such as when smiling or laughing. Static dimples are rare formations visible even when the face is entirely at rest.
The chin dimple, commonly known as a cleft chin, is a separate anatomical category with a different origin than cheek dimples. This Y-shaped indentation results from an incomplete fusion of the two sides of the lower jawbone, or mandible, during fetal development. Unlike the muscle-based cause of cheek dimples, the cleft chin is a structural feature that remains visible regardless of facial expression.
A different form of chin dimpling, often called a “pebble chin” or peau d’orange (orange peel skin), is caused by the overactivity of the mentalis muscle. This muscle attaches directly to the chin skin. When it contracts excessively, it creates a bumpy, pitted texture rather than a single, distinct cleft.
Dimples Found Elsewhere on the Body
Dimples are not exclusively a facial feature; small indentations can also appear on the lower back, often referred to as Dimples of Venus. These paired indentations are located just above the buttocks, directly over the sacroiliac joints. The formation of these back dimples is entirely structural and does not involve the facial muscle variations seen in cheek dimples.
The Dimples of Venus are created by a short, fibrous ligament that stretches between the skin and the posterior superior iliac spine, a bony prominence on the pelvis. This ligament tethers the skin tightly to the underlying bone structure, causing the visible depression. Their prominence is often influenced by factors like body fat percentage and skeletal structure.
Another distinct type is the single sacral dimple, which appears as a midline indentation located in the crease just above the buttocks. While most sacral dimples are benign, a deep, large, or unusually located one can occasionally be a superficial marker for an underlying spinal column irregularity. These atypical presentations are sometimes associated with conditions like spina bifida occulta, which involves incomplete closure of the bone surrounding the spinal cord.
How Dimples Are Inherited
The inheritance of facial dimples is a complex genetic trait still being explored by researchers. Historically, dimples were often taught as a simple autosomal dominant trait, meaning only one copy of the gene was required for expression. However, current understanding suggests a more nuanced, polygenic model of inheritance.
The expression of dimples is now thought to be influenced by multiple genetic variants, rather than a single dominant gene. This polygenic influence helps explain why the inheritance pattern is often unpredictable, sometimes skipping generations or appearing in children whose parents do not have them. The exact gene or combination of genes responsible for the Zygomaticus Major variation remains unidentified.
Even structurally caused dimples, such as the cleft chin or Dimples of Venus, are considered hereditary traits that run in families. While the anatomical mechanism is known, the genetic pathway dictating the incomplete jaw fusion or the short ligament formation is also passed down through generations.