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Ah, one of the great mysteries of life! Searches on "belly button" and related phrases revealed that no one knows for sure why some people have a concave belly button while others have one that sticks out. Health and parenting web sites agree that most people have "innies" and only about 10% of the population has "outies." But neither button style has any effect on health.
The belly button is a tangible reminder that we were all intimately connected to our mothers at one time. Oxygen and nutrients travel from mom to baby through the umbilical cord, and when the baby is born, this cord is clamped off and cut. That leaves a tiny stump that dries up and falls off a few weeks after birth and usually leaves a concave scar we call a belly or tummy button. Sometimes, the scar pokes out from the stomach, resulting in an "outie." As numerous sources including BBC Health and Blue Cross Blue Shield of Minnesota report, whether you end up with an innie or an outie is random.
Nikon MicroscopyU suggests that extra skin left from the umbilical cord may cause the protrusion of an outie, and the Queensland Science Teachers Network says the difference between innies and outies is due to where the umbilical cord is cut. But these are the only sources we found that offered such explanations. A doctor quoted in one Salon column notes that the umbilical cord is always clamped several inches away from the navel and doesn't affect innie or outie status.
A more popular theory about outies is that they are caused by umbilical hernias. This condition is due to a small circular defect in the baby's abdominal wall that can make the belly button protrude. ParentSoup estimates that 10% to 30% of babies are born with umbilical hernias, but most heal as the abdominal muscles grow during a baby's first few years. However, American Baby says not to confuse an umbilical hernia with an outie belly button. A hernia expands when the baby cries or strains, but an outie doesn't. Also, the Cleveland Clinic's picture of an umbilical hernia looks a lot more protuberant than a standard outie.
With low-rise pants and cropped tops all the rage, belly buttons have been getting a lot of media attention. People who are unhappy with their outies are even having plastic surgery. But we say if you have an outie, flaunt it.
