The umbilicus, commonly known as the belly button, is simply a scar on the abdomen. This unique feature marks the site where the umbilical cord once connected a developing fetus to the placenta, providing necessary nourishment and waste removal during gestation. Navel shape varies significantly among individuals, ranging from deep indentations to slight protrusions, with a flat appearance being one of the many normal anatomical variations.
The Origin Story of the Navel
The navel’s initial form is determined immediately after birth when the umbilical cord is clamped and severed. The remaining stump, a mix of connective tissue and blood vessels, undergoes a natural process of drying and necrosis over the next one to two weeks. As the stump detaches, the underlying tissues contract and the skin around the umbilical ring begins to heal, forming a permanent fibrous scar tissue known as the cicatrix.
The resulting shape is largely a matter of how the skin fuses to the deeper abdominal fascia at the umbilical ring. If the residual scar tissue is tightly bound and relatively short, it pulls the skin inward, creating the common “innie” appearance. A flat navel results when this fibrous connection is broad and strong, anchoring the skin flush against the abdominal wall without creating a significant inward depression or outward projection.
Primary Factors Determining Navel Shape
The way the underlying connection healed is the foundational element, but the amount of subcutaneous tissue around it significantly modifies the visible shape. A high accumulation of abdominal fat, or adiposity, can fill in any slight depression, making a mildly concave navel appear completely flat or even slightly protruding.
The tension and condition of the abdominal muscles, particularly the rectus abdominis, also play a role in navel appearance. These muscles meet at the midline, directly beneath the navel, and their tone influences the firmness of the abdominal wall. A strong, tight abdominal wall can contribute to a taut, flat appearance, especially when the underlying fibrous connection is already broad. Conversely, muscle weakness can sometimes alter the contour of the surrounding skin, indirectly affecting how the navel is displayed.
When a Flat Navel Indicates a Medical Condition
While a flat navel is often a normal anatomical variation, a change in shape can sometimes be the result of a past medical procedure or physical change.
Surgical Interventions
One common cause is the surgical repair of an umbilical hernia, a condition where internal tissue pushes through a weak spot near the navel, often resulting in an “outie.” During a herniorrhaphy, the surgeon secures the abdominal wall, which naturally flattens the area and often converts a protruding navel into a flat one. A flat or newly reshaped navel can also be the outcome of cosmetic surgery, such as an abdominoplasty or “tummy tuck.” This procedure involves the repositioning and refinement of the navel to create a flatter contour on the newly tightened abdominal skin.
Body Changes
Rapid or extreme body changes, such as significant weight loss or the stretching of the abdomen during pregnancy, can also cause the navel to flatten. The intense pressure and skin distension during the third trimester of pregnancy can temporarily or sometimes permanently stretch the skin and fascia, smoothing out a previously deep indentation.