Whether or not you have an outie or innie belly button is a question of chance. After you are born, your umbilical cord is cut and then becomes an umbilical stump. When this stump falls off, what remains is your final umbilical scar — your belly button. This belly button may protrude (outie) or recede inwards (innie). For around 10% of the population belly button scars become outie belly buttons.
In most cases the difference between the two is simply aesthetic, but sometimes an outie can be caused by an umbilical hernia – this is where a weakness in the abdominal wall allows the intestines to push through and put pressure on the umbilicus. Umbilicoplasty can work to repair this.