The indentations found on the lower back, often referred to as “butt dimples,” are a common and entirely natural anatomical feature. These small, symmetrical depressions are a visible manifestation of the underlying structure of the pelvis. Their presence is predetermined by genetics and relates directly to how the skin attaches to the deeper skeletal framework. Understanding the specific anatomy of this region reveals why these indentations form and what makes them appear more or less noticeable.
What Are Dimples of Venus and Apollo?
The symmetrical indentations located just above the upper curve of the buttocks are informally known as the Dimples of Venus in women and the Dimples of Apollo in men. These names are ancient, referencing the Roman goddess and god of beauty, respectively.
These paired depressions are situated directly over the sacroiliac joints, where the sacrum—the triangular bone at the base of the spine—connects to the ilium, the largest bone of the pelvis. The proper anatomical term for these indentations is the fossae lumbales laterales, or lateral lumbar indentations. They are a purely superficial topographical feature, meaning they are a variation in surface appearance rather than a medical condition.
The Anatomy Behind the Indentations
The existence of these dimples is directly attributed to short, fibrous connective tissues that anchor the skin to the underlying bone. These ligaments stretch from the skin’s dermal layer down to the posterior superior iliac spine, a bony prominence on the back of the pelvis. This tight attachment effectively pulls the skin inward at that specific point.
The surrounding area lacks a significant amount of muscle tissue, which contributes to the indentation’s visibility. In many areas of the body, muscle bulk or a uniform layer of subcutaneous fat would smooth out such an anchor point. Because this area is relatively sparse in both deep muscle and major fat pads, the tension created by the short ligament is clearly seen on the surface.
The presence and prominence of these connecting ligaments are genetically determined. If an individual is not predisposed to having them, they cannot be created through exercise or other lifestyle changes. The dimples are present from birth, and they serve as a precise external landmark for the location of the sacroiliac joints, a point sometimes referenced by surgeons during spinal procedures.
When Dimples Indicate a Medical Issue
It is important to distinguish the bilateral Dimples of Venus or Apollo from a different, singular indentation sometimes found in the same general region: the sacral dimple, or fovea. The Dimples of Venus are symmetrical, lie on either side of the spine over the pelvic bones, and have no medical consequence. A sacral dimple, conversely, is a single pit or indentation located directly on the midline, just above the crease of the buttocks.
While most sacral dimples are shallow and harmless, they occasionally require medical evaluation as they can be a subtle marker for an underlying spinal column defect. In rare instances, a deep sacral dimple may be associated with conditions like spina bifida occulta, where the vertebrae do not completely close around the spinal cord, or tethered cord syndrome.
Certain accompanying features around a sacral dimple raise suspicion and warrant a doctor’s assessment. These warning signs include a tuft of hair growing from the site, a skin tag, or an area of skin discoloration. A simple, shallow sacral dimple without these associated external signs is typically benign. Differentiation between the two types is based on location, number, and depth.
Factors That Affect Dimple Prominence
While the presence of the dimples is rooted in genetics, their degree of visibility is influenced by individual body composition. The amount of subcutaneous fat in the lower back region is the primary factor determining how noticeable the indentations are. A lower body fat percentage generally allows the skin to lie closer to the underlying ligaments, which accentuates the inward pull and makes the dimples more defined.
Conversely, a higher amount of fat in the lower back can fill out the skin’s surface, masking the tethered connection and making the dimples less obvious or even completely invisible. Developing the surrounding muscles, such as the gluteal muscles and lower back extensors, can also create a contrasting effect. Toning these adjacent muscle groups causes the surrounding tissue to slightly protrude, making the fixed, anchored spot of the dimple appear more indented and prominent.