A dimple is a small, visible indentation in the skin, resulting from variations in the underlying anatomy, specifically in the muscles or connective tissues. While commonly associated with a smiling face, dimples can appear in several different locations across the body. This article investigates the distinct anatomical causes and various places these natural grooves can be found.
The Anatomy of Dimple Formation
Dimples are inherited. They are an autosomal dominant trait, meaning only one copy of a specific gene may be required for the trait to be present. The inheritance pattern can be variable, however, with the appearance or disappearance of dimples sometimes occurring over time or skipping generations.
The physical indentation results from a tethering effect, where the skin is pulled inward by a shorter or split underlying structure. In facial dimples, this structure is usually a muscle, while in other body locations, it involves ligaments or bone structure. This tethering mechanism creates a depression that becomes more pronounced when the surrounding tissue is moved or contracted. The depth and visibility of any dimple can be influenced by the amount of subcutaneous fat in the area.
The Most Common Facial Dimples
Cheek dimples, known medically as fovea buccalis, appear on the side of the mouth, usually becoming visible when a person smiles. They are caused by a variation in the zygomaticus major muscle, which is the primary muscle responsible for pulling the corner of the mouth upward and outward when smiling.
In people with cheek dimples, the zygomaticus major muscle is often bifid, meaning it splits into two separate bundles near its insertion point. One muscle bundle attaches at the corner of the mouth, while the other attaches below it and is tethered to the overlying dermis, or skin layer. When the muscle contracts during a smile, this tethering action pulls the skin inward, creating the characteristic depression. While it is possible to have a dimple on only one cheek (unilateral), having a dimple on both sides (bilateral) is more common.
Exploring Rare and Unusual Locations
Beyond the cheeks, dimples can occur in other locations, each with its own distinct anatomical cause. The mechanisms for these less common dimples are fundamentally different from the muscle variation that causes a cheek dimple.
Chin Dimples (Cleft Chin)
A chin dimple, often called a cleft chin or fovea mentalis, is a Y-shaped indentation found in the center of the chin. Unlike cheek dimples, a cleft chin is typically a static feature, remaining visible even when the face is at rest. This indentation is a result of a variation in the underlying jaw structure.
During fetal development, the left and right halves of the lower jawbone, or mandible, grow together and fuse in the midline. A chin dimple occurs when this fusion is incomplete, leaving a small gap or fissure in the bone or the overlying muscle. The skin then adheres to this small depression, creating the indentation on the chin’s surface.
Dimples of Venus (Back Dimples)
Symmetrical indentations on the lower back, just above the buttocks, are known as the Dimples of Venus, or fossae lumbales laterales. These dimples are positioned directly over the sacroiliac joints, where the sacrum attaches to the pelvis. Their cause is not muscular but ligamentous.
These depressions are formed by a short ligament that connects the skin directly to the underlying bone, specifically the posterior superior iliac spine of the pelvis. This ligament creates a permanent tethering effect that pulls the skin inward. The visibility of the Dimples of Venus is significantly affected by the distribution of body fat in the lower back area.
Other Rare Facial Locations
While cheek and chin dimples are the most noted, other facial dimples can occur around the mouth. These can include indentations immediately above or below the corners of the mouth, sometimes referred to as para-angle dimples. These variations are less common and relate to variations in the insertion points of the facial muscles surrounding the mouth.
Extremely rare occurrences, such as a dimple on the forehead or a single, deeper dimple on one cheek, highlight the diversity of anatomical variations.