A dimple on the stomach, or abdomen, is a common physical trait that often sparks curiosity about its origin. An abdominal dimple is defined as a small, localized depression or indentation on the skin’s surface. This feature is typically benign, representing a variation in the underlying tissue layers. Understanding why these depressions form requires looking closely at the anatomy of the abdominal wall. The causes range from a normal scar left over from birth to unique arrangements of fat and connective tissue, and in rare cases, signs of a medical condition.
Understanding the Navel: The Most Common Abdominal Indentation
The most frequent reason for a dimple on the abdomen is the navel, medically known as the umbilicus. This indentation is a scar left by the umbilical cord after it is cut at birth. The cord, which provided oxygen and nutrients during fetal development, leaves behind a small stump that shrivels and eventually falls off, with the resultant healing process determining the final shape of the scar.
The appearance of the navel is largely determined by how the remaining scar tissue heals and integrates with the surrounding abdominal structures. The two primary variations are the “innie,” which is a small inward fold or depression, and the less common “outie,” a slight outward protrusion. The vast majority of people, approximately 90%, have an innie navel.
The depth and appearance of an innie navel are influenced by the amount of scar tissue that pulls inward during healing. The underlying structure of the abdominal wall and the amount of surrounding subcutaneous fat also play a role in shaping the final indentation. Changes in body weight or pregnancy can alter the surrounding skin and fat tissues, which may temporarily or permanently change the navel’s shape.
Anatomical Reasons for Other Abdominal Indentations
Dimples that occur elsewhere on the abdominal surface, outside of the navel, are usually a result of normal anatomical variations in the connective tissue. The abdominal wall consists of several layers, including skin, a superficial fatty layer, and a deeper layer of connective tissue known as fascia. This fascia acts as a supporting structure, helping to anchor the skin to the underlying muscle.
Localized indentations can form where the fibrous septa, which are bands of connective tissue, are particularly short or dense, tightly attaching the skin to the fascia beneath it. This tight tethering creates a point of depression on the surface, especially when the surrounding tissue is pushed inward or when the abdominal muscles are flexed. The presence and visibility of these anchor points are often influenced by genetics.
A person’s localized fat distribution also impacts how pronounced these indentations appear. The superficial fatty layer is organized into lobules, and the arrangement and size of these fat cells vary across the abdomen. When a person gains or loses weight, the change in the volume of fat surrounding a tightly anchored spot can make the natural depression more noticeable.
Surgical history can also contribute to a localized dimple or depression. Any incision that penetrates the abdominal wall, such as for an appendectomy or C-section, leaves behind a scar that includes the underlying fascia. The healing process can cause the skin to adhere to the deeper layers of muscle or fascia, resulting in an indentation around the surgical site.
When a Dimple Requires Medical Attention
While most abdominal dimples are harmless anatomical features, a new or changing indentation sometimes signals an underlying medical concern. One of the most common issues that can present as a noticeable change is a hernia, where an organ or tissue pushes through a weak spot in the abdominal muscle or tissue. Umbilical hernias occur near the navel, while incisional hernias occur at the site of a previous surgical scar.
A hernia often manifests as a bulge or a soft lump that may sometimes be mistaken for an indentation when the surrounding area swells. This condition may be accompanied by pain, particularly when coughing, bending, or lifting heavy objects. The difference between a benign dimple and a hernia is that a hernia often feels like a mass protruding outward, and in some cases, it can be gently pushed back into the abdomen, a characteristic known as reducibility.
Other soft tissue masses, such as a lipoma, can also cause a depression or lump. A lipoma is a benign tumor made of mature fat tissue that develops just beneath the skin. These masses are typically soft, rubbery, and slow-growing, and they are usually mobile when pressed.
There are specific warning signs that indicate the need for prompt medical consultation. These include a dimple or lump that rapidly increases in size, becomes painful, or is accompanied by systemic symptoms like fever, nausea, or vomiting. A mass that cannot be pushed flat, known as an irreducible hernia, requires immediate attention, as it may indicate a potentially serious complication like bowel obstruction or strangulation.