The navel, or umbilicus, is the permanent scar remaining after the umbilical cord detaches from a newborn. The cord connects the fetus to the placenta, supplying oxygen and nutrients during gestation. Once the cord is clamped, the remaining stump dries and falls off, typically within one to two weeks, forming the belly button. Navels are categorized by appearance: the concave form is an “innie,” and the less frequent, convex form is an “outie.”
The Prevalence of Navel Types
The vast majority of people have an “innie” navel, which is the common shape across the global population. Current estimates indicate that only about 10% of individuals develop an “outie” belly button. This means that for every person with a protruding navel, there are nine with a recessed one. Both forms represent normal variations of the healed scar left by the umbilical cord.
How the Navel Shape is Determined
The final shape of the navel is determined by the body’s natural process of scar formation and the underlying anatomy. When the umbilical stump detaches, the remaining tissue is remodeled into a scar composed of dermis and underlying fascia. The degree to which this scar tissue retracts or protrudes dictates the ultimate appearance of the umbilicus.
Factors in the healing process include the location where the cord inserted and the amount of scar tissue produced. Extra scar tissue, or the way the skin adheres to the abdominal fascia, can result in the skin pushing outward slightly. Conversely, the retraction of the abdominal wall musculature and the tightening of the umbilical ring create a concave appearance.
There is a common misconception that the navel’s shape results from how the attending physician cuts or ties the umbilical cord. This idea is anatomically incorrect; external manipulation of the cord has no bearing on internal scar tissue formation. The umbilical cord is clamped and cut a few inches from the body. The subsequent healing of the stump is a biological process governed by genetics and individual healing patterns, making the resulting shape a matter of chance, not medical technique.
When an Outie Signals a Medical Concern
While most outie navels are simply a result of normal anatomical variation, a prominent or protruding navel can sometimes indicate an underlying medical condition. The most frequent cause for a pronounced outie, especially one that changes size, is an umbilical hernia. This condition occurs when a portion of the intestine or fatty tissue pushes through a weakness in the abdominal wall near the navel.
In infants, umbilical hernias are relatively common and often present as a soft bulge that becomes more noticeable when the baby cries or strains. A majority of these hernias in children close spontaneously by the age of two, as the abdominal muscles naturally strengthen and grow together. If the protrusion does not resolve itself by the time a child is five, doctors may recommend intervention.
In adults, hernias are less likely to resolve on their own. They may be caused by increased abdominal pressure due to pregnancy, obesity, or chronic coughing. Parents or adults should consult a physician if a protruding navel is accompanied by pain, tenderness, redness, or warmth. These symptoms could signal a serious complication where the protruding tissue is trapped and blood flow is restricted.