A belly button, also known as the navel or umbilicus, is a scar on the abdomen. This scar marks the site where the umbilical cord once connected a developing fetus to its mother. Belly buttons exhibit various shapes and sizes, with the most common distinctions being an “innie” (concave) or an “outie” (protruding). These variations are a natural part of human anatomy.
Understanding Belly Button Formation
During pregnancy, the umbilical cord serves as a lifeline, delivering oxygen and nutrients from the mother’s placenta to the fetus and carrying away waste products. Shortly after birth, healthcare professionals clamp and cut this cord, a painless procedure for both mother and baby. This leaves behind a short piece of tissue known as the umbilical stump, which typically dries and detaches over one to three weeks, leaving the scar that becomes the belly button.
The Anatomy Behind Innies and Outies
The shape of a person’s belly button, whether an innie or an outie, is primarily determined by how the umbilical stump heals and the resulting scar tissue. For an “innie,” the scar tissue tends to retract slightly inward, or by surrounding fat tissue pulling it inward. Approximately 90% of people have an innie belly button. This inward appearance is largely a matter of chance and not influenced by how the umbilical cord was cut or cared for.
Conversely, an “outie” occurs when scar tissue or skin protrudes outward. It can also be influenced by the underlying abdominal muscle structure. While less common, with about 10% of individuals having an outie, it is generally considered a normal anatomical variation. Occasionally, an outie might result from an umbilical granuloma, which is extra tissue forming around the healing stump, or a small umbilical hernia where abdominal contents push outward.
When to Consult a Doctor
While most outies are normal, a protruding navel can sometimes indicate an umbilical hernia. An umbilical hernia happens when a part of the intestine or abdominal fat bulges through a weak spot in the abdominal muscles near the navel. These hernias are common in infants and often resolve on their own as the abdominal muscles strengthen, typically by age two.
In adults, umbilical hernias are also possible and may cause discomfort. You should consult a doctor if you notice a bulge near your navel that is accompanied by pain, tenderness, or discoloration of the surrounding skin. Seek immediate medical attention if the bulge becomes severely painful, firm, or if you experience vomiting or difficulty passing gas or stool, as these could signal a medical emergency like a strangulated hernia.