The navel, or umbilicus, is the small scar on the abdomen remaining after birth. This scar marks the site where the umbilical cord connected the fetus to the placenta. Navels exhibit a wide range of shapes, commonly classified as an “innie” or an “outie.” A deep belly button is a variation of the “innie” type, representing a significant indentation relative to the surrounding abdominal surface. The depth of this feature is determined not by how the cord was cut, but by the foundational scar tissue and the anatomy of the surrounding abdominal wall layers.
The Embryological Origin of the Navel
The journey to forming the navel begins during gestation, where the umbilical cord connects the developing fetus to the mother. This cord contains blood vessels that facilitate biological exchange until birth. After delivery, the cord is clamped and cut, leaving a small stump of tissue and vessels.
This remaining stump undergoes necrosis and separation, typically detaching within five to fifteen days after birth. The resultant structure is a cicatrix, which is dense, fibrous scar tissue formed by the contraction and epithelialization of the underlying umbilical ring. The exact appearance of this initial scar is influenced by the body’s natural healing process and developmental factors, not the location of the initial cut or clamp.
The foundational scar tissue of the navel is a weak point in the anterior abdominal wall. How the surrounding tissues involute—or contract and fold inward—determines the initial shape. While the cord detaches, the internal remnants of the blood vessels seal off and morph into suspensory ligaments within the abdomen. The depth of the resulting navel is a consequence of the scar’s position relative to the abdomen’s contours as the body heals.
Anatomical Factors Determining Navel Depth
A deep belly button is an appearance created by the volume and distribution of the tissues surrounding the scar. The most influential factor determining navel depth is the amount of subcutaneous adipose tissue, the layer of fat situated directly beneath the skin. Higher amounts of this fat surrounding the navel can cause the scar tissue to appear sunken or inverted.
This effect occurs because the navel’s scar tissue is relatively fixed, but the surrounding abdominal wall can accumulate significant volume. The abdominal subcutaneous tissue comprises a superficial and a deep adipose layer separated by a membranous layer of fascia. When the fat lobules in these layers expand, they push the skin outward, creating a valley effect where the fixed scar tissue resides.
The underlying abdominal fascia and muscle tone also play a role in establishing the navel’s depth. The fascia is a multilayered sheet of connective tissue that provides structural support for the fat and the abdominal wall. The tension and structure of this tissue, including the rectus abdominis muscles, influence how tightly the umbilical scar tissue is pulled inward. Variation in fat deposition and fascial structure is often linked to genetically predetermined body types.
Modifications to Navel Depth Over the Lifespan
While the initial scar forms the permanent structure of the navel, its depth and appearance are subject to modification throughout life due to changes in body volume. Weight fluctuation is the most common factor that alters the perceived depth. A substantial gain in weight increases the volume of subcutaneous fat, which can make the navel appear deeper as the surrounding tissue expands and effectively “buries” the scar.
Conversely, major weight loss can have a variable effect, either deepening the navel if surrounding fat is reduced or making it appear shallower if the skin loses elasticity and stretches. Pregnancy is another factor that temporarily changes navel depth due to the internal pressure from the expanding uterus. This pressure pushes the entire abdominal wall forward, often flattening a deep navel or causing an innie to become a temporary outie during the second or third trimester.
The navel typically returns to its original shape and depth following delivery, although the stretched skin and abdominal wall may lead to a slightly altered appearance. These changes demonstrate that while the navel’s scar tissue is a fixed point, its perceived depth is a dynamic measurement relative to the volume and tension of the skin and fat layers of the abdomen.