The reason you have an innie or outie belly button

In our opinion, belly buttons are one of the human body's more odd-looking parts. Though "innie" belly buttons are more common than "outie" belly buttons, no shape or size of belly button is considered to be more normal or better than the other (via NBC News). But that doesn't stop us wondering why some people have an "innie" and others have an "outie."

The answer is actually quite simple. According to Healthline, belly buttons, also known as navels, mark where your umbilical cord once was. When the umbilical cord is cut, the leftover cord heals itself in the same way as a scar, and naturally turns inwards or outwards.

Belly buttons naturally grow inwards or outwards

Referring to an "outie" belly button, Jennifer Shu, M.D., FAAP, an Atlanta pediatrician, co-author of Heading Home With Your Newborn: From Birth to Reality, and spokesperson for American Academy of Pediatrics, told Real Simple, "The skin just chooses to grow in an outward direction rather than inward." 

Dr. Curtis Cetrulo, Jr., a plastic surgeon at Massachusetts General Hospital in Boston, agrees, explaining to NBC News that the amount of space between the skin and the abdominal wall often determines which way your belly button will grow. If there is less space, soft tissue will most likely protrude through, pushing the remaining umbilical outwards and ultimately creating an "outie" belly button.

Women may notice their belly button pop out when pregnant

Pregnant women often notice their "innie" belly button pop out or become an "outie" as their bump grows bigger, but for the rest of us, belly buttons remain in the same in shape and size for the duration of our lives. 

Certulo notes that he sees many patients who request umbilicoplasty (belly button surgery) to transform their belly button into their desired shape. However, this is purely for cosmetic reasons. Interestingly, he has only ever had patients asking for an "innie" belly button, with many requesting "a vertical dime slot of a belly button that's small and thin," rather than an "outie."