The navel, or umbilicus, is a permanent scar marking where the umbilical cord connected a person to their mother during gestation. Navels vary widely in shape, size, and depth, often categorized as an “innie” or an “outie.” The horizontal belly button appears as a wide, transverse slit or oval. Its orientation is determined by the initial healing process and the subsequent physical forces acting on the abdominal wall throughout life.
The Scarring Process That Creates the Navel
The navel begins after birth when the umbilical cord is clamped and severed, leaving a small stump. This stump dries out and detaches within one to two weeks, leaving a small wound. The resulting structure is a cicatrix, the medical term for fibrous scar tissue that forms as the umbilical ring closes through contraction and collagen deposition.
The initial shape is determined by how the skin and underlying fascia heal in infancy. Most people develop an “innie” where the scar tissue retracts inward. The exact contours—round, vertical, or horizontal—are set during this early developmental scarring, providing the foundational structure upon which later life factors will act.
Body Structure Influences on Horizontal Orientation
The horizontal appearance of the navel is primarily dictated by constant tension and pressure exerted by surrounding abdominal structures. The umbilical scar is a relatively weak point in the abdominal wall, making it susceptible to distortion from internal and external forces. This mechanical stress pulls the navel into a wider, flatter shape over time.
The distribution of subcutaneous fat is a significant factor. Excess adipose tissue around the midsection presses against the navel’s skin folds, stretching the opening laterally and contributing to a shallower, horizontal appearance. Additionally, the underlying abdominal musculature applies horizontal tension to the skin. This tension pulls the fixed scar tissue sideways, effectively flattening the opening.
The inherent elasticity of the skin and surrounding connective tissue also plays a role. Skin with less elasticity may stretch more broadly in response to pressure, widening the navel into a horizontal oval instead of maintaining a vertical slit. This interplay between muscle tension, fat distribution, and skin quality shapes the navel’s final orientation.
Changes in Navel Appearance Over Time
The navel is not a static feature and its appearance can change significantly throughout life, particularly due to changes in abdominal volume and internal pressure. Significant weight fluctuations, both gain and loss, can alter the navel’s shape by stretching the surrounding skin and fascia. Weight gain often causes the navel to appear wider and more horizontal as the abdominal wall expands.
Pregnancy is another influence, as the expanding uterus places pressure on the abdominal wall, often causing an “innie” to temporarily flatten or push outward. While the navel often returns to its pre-pregnancy state, it may appear wider or more horizontal due to the stretching of the skin and fibrous tissue.
A change in navel appearance can sometimes indicate an umbilical hernia, where internal tissue pushes through the weak spot. If the navel develops a painful, hard, or growing bulge, or is accompanied by severe abdominal pain, nausea, or vomiting, seek medical advice for evaluation.