Innies are far more common than outies. About 90% of people have an innie belly button, while only about 10% have an outie. Any belly button that curves inward is classified as an innie (concave), and any that protrudes outward is an outie (convex).
What Determines Your Belly Button Shape
A common myth is that the way a doctor or midwife cuts or clamps the umbilical cord decides whether you end up with an innie or an outie. That’s not true. After birth, two clamps are placed on the cord, and it’s snipped between them. The remaining stump dries up and falls off within a few weeks, leaving behind a scar. That scar is your belly button, and the clamping and cutting process has nothing to do with its final shape.
Instead, your belly button shape comes down to how your skin and underlying tissue heal after the stump detaches. When the tip of the umbilical cord’s remnant pokes out past the surrounding skin, you get an outie. It’s simply normal human variation, similar to having curly hair or dimples. There’s no single gene or technique that controls it.
Belly Button Shapes Beyond Innie and Outie
The innie-outie distinction is actually a simplification. Plastic surgeons use a classification system called SHAPE that describes navels by their specific contour: vertical oval, horizontal oval, round, or T-shaped. Most people’s belly buttons fall somewhere along this spectrum rather than fitting neatly into one of two categories.
When it comes to what people find most attractive, preferences differ by sex. Research published in Aesthetic Plastic Surgery found that the ideal female navel is a vertical oval, while the ideal male navel is a horizontal oval (with the horizontal dimension about 10 to 20% wider than the vertical). The shape rated least attractive by a wide margin was the protruding outie, chosen as the least appealing by 48% of survey respondents.
When an Outie Signals Something Else
Most outies are purely cosmetic and harmless, but in infants, a protruding belly button sometimes indicates an umbilical hernia. This happens when a small section of tissue or intestine pushes through a weak spot in the abdominal wall near the navel. The bulge becomes more noticeable when the baby cries, coughs, or strains. Pediatric umbilical hernias are common and usually close on their own by age 4 or 5 without treatment.
Another condition that can mimic an outie in newborns is an umbilical granuloma, a small, round piece of moist red tissue that forms after the cord stump falls off. It occurs in about 1 out of every 500 babies. A granuloma isn’t painful, but it can cause minor bleeding or drainage and typically needs simple treatment to resolve.
Research has also found that navel shape at birth may predict hernia risk. Infants born with a protruding or crescent-shaped belly button are more likely to develop persistent umbilical hernias than those with the standard concave shape. More than 60 normal anatomical variations of the umbilicus have been identified.
Can Your Belly Button Change Shape?
Yes, and pregnancy is the most common reason. As the uterus expands, it puts increasing pressure on the abdominal wall, and many people with innies watch their belly button pop out or flatten completely. This typically happens around 26 weeks, in the second or third trimester. It’s harmless, and the belly button almost always returns to its original shape after delivery.
Significant weight gain or loss can also alter belly button appearance over time. Abdominal surgeries, particularly those involving incisions near the navel (like laparoscopic procedures), can reshape it as well. For people who want to change their belly button cosmetically, a procedure called umbilicoplasty can reconstruct it into a preferred shape.