Indentation on the skin of the buttock or lower back are common observations that prompt many people to seek an explanation. These depressions vary in location, size, and depth, and they have entirely different anatomical origins. The presence of dimples indicates one of several distinct phenomena related to the structure of skin, fat, and underlying bone. Understanding the specific location and nature of the indentation helps determine if it is a harmless genetic trait, a structural characteristic, or a rare medical anomaly.
Anatomical Indentations: The Dimples of Venus
The pair of symmetrical indentations seen on the lower back, just above the curve of the buttocks, are known as the Dimples of Venus. This feature is a purely anatomical marker with no association with health, diet, or exercise. These dimples are positioned directly over the sacroiliac joints, where the sacrum connects to the ilium of the pelvis.
Their formation is linked to a short, fibrous ligament that stretches from the skin’s surface down to the posterior superior iliac spine, a bony prominence on the pelvis. This ligament tethers the skin at that specific point, creating the depression. Since this is an inherited trait determined by genetics, it is present from birth.
The visibility of the Dimples of Venus is affected by the amount of fat in the lower back area. Less surrounding tissue can make the tethered point more pronounced, but the underlying anatomical structure remains fixed. They are sometimes referred to by their Latin name, fossae lumbales laterales, or lateral lumbar indentations, in medical contexts.
Dimpling Caused by Connective Tissue Structure
The most common form of dimpling, often referred to as a “cottage cheese” or “orange peel” texture, occurs in the subcutaneous fat layer. This characteristic dimpling is caused by the interaction between fat cells and the fibrous connective tissue, known as septae, that runs through the fat layer. These septae are composed primarily of collagen and anchor the skin to the deeper fascia or muscle below.
In areas prone to this dimpling, such as the buttocks and thighs, the septae tend to be arranged in a vertical pattern. When fat cells expand, they push upward against the skin, but the rigid, vertical septae hold the skin down at various points. This creates an uneven surface texture where the fat bulges between the points tethered by the stiff bands.
The architecture of this connective tissue is why this texture is seen far more frequently in women, affecting an estimated 80% to 98% of postpubertal women. In men, the fibrous septae are often arranged in a crisscross or diagonal pattern, creating a more supportive structure that resists the outward pressure of fat cells. Hormonal factors, particularly estrogen, also influence fat distribution and contribute to the development of this texture.
The appearance of this dimpling is affected by factors like skin thickness, body fat percentage, and circulation. However, the underlying structural cause is the tethering effect of the fibrous septae. It is considered a normal structural variation, not a disease or a condition strictly related to obesity. Treatments that successfully reduce the dimpled appearance often work by physically or chemically releasing the tension of these septae.
When Dimples Require Medical Attention
A different type of dimple, called a sacral dimple, is a congenital indentation that appears near the tailbone, just above the crease between the buttocks. These are present at birth and are typically shallow, occurring in a small percentage of newborns. Most sacral dimples are entirely benign and pose no health concern, requiring no treatment.
However, a sacral dimple can occasionally indicate an underlying spinal issue, such as spina bifida occulta or tethered cord syndrome. This involves the spinal cord not hanging freely within the spinal canal. Medical attention is warranted if the dimple exhibits characteristics suggesting a deeper connection to the spine.
A physician should evaluate the dimple if it is unusually large, very deep, or accompanied by other skin features. Concerning signs include an associated patch of hair, a skin tag, a fatty lump, or an area of discoloration nearby. In these cases, imaging tests like an ultrasound or MRI may be recommended to ensure the spinal cord is developing normally. The presence of drainage or swelling around the dimple also requires immediate medical review.