The appearance of a belly button, or navel, is a common source of curiosity for new parents. The terms “innie” and “outie” are informal descriptions used to classify whether the navel is concave or protrudes outward. This feature is essentially a scar marking the former connection point between the mother and the developing fetus. While the final outcome of the navel’s shape is often a matter of chance, understanding the underlying biology clarifies why these variations occur in the general population.
The Formation of the Belly Button
The belly button is the physical remainder of the umbilical cord, which supplied oxygen and nutrients from the placenta to the fetus. After birth, the cord is cut, leaving a small stump attached to the baby’s abdomen. This stump lacks nerve endings, making the procedure painless for the newborn. Over the next one to three weeks, the remaining stump dries and shrivels, a process known as mummification. The tissue darkens and shrinks before detaching completely, leaving a small wound that heals into the final scar tissue of the belly button.
The Truth About “Innies” and “Outies”
The final appearance of the belly button is largely determined by the nature of the healing process. An innie, the more common shape, occurs when the scar tissue contracts inward as it heals, creating a concave depression. The way the skin and muscle around the cord site attach also influences the depth and overall appearance of the navel.
An outie, which occurs in an estimated 10% of the population, results from the scar tissue or skin folding outward rather than adhering inward. This is a normal variation and is not caused by the doctor’s clamping technique or how the stump was cared for. The shape is simply a consequence of how the skin naturally heals, potentially influenced by genetic factors affecting skin elasticity.
Medical Conditions That Cause an “Outie” Appearance
While most outies are simply a cosmetic variation, a protruding navel can sometimes be caused by two common medical conditions that manifest during infancy.
Umbilical Granuloma
An umbilical granuloma is a small, soft, reddish lump of moist tissue that forms after the umbilical stump falls off. This is an overgrowth of scar tissue at the base of the navel, which may produce a clear or yellowish discharge. Granulomas are benign and often resolve on their own within a week or two, but they can be easily treated if they persist. Treatment typically involves applying silver nitrate to chemically burn off the excess tissue, a painless procedure since the growth lacks nerves.
Umbilical Hernia
Another potential cause for a protruding belly button is an umbilical hernia. This occurs when a small portion of the intestine or fatty tissue pushes through a weak spot in the abdominal muscle wall near the navel. The hernia appears as a soft bulge that may become more noticeable when the baby cries, coughs, or strains. Umbilical hernias are common in newborns and are generally harmless, often closing spontaneously by the time the child is one or two years old. Parents should seek medical attention if the bulge becomes hard, discolored, or if the baby shows signs of pain, indicating a rare complication where tissue becomes trapped.