It sits right in the middle of your stomach, collects the occasional bit of lint, and gets poked by curious toddlers. The belly button is one of the most familiar parts of the body. But have you ever stopped to wonder why it's there at all?
Your belly button is a scar. It marks the spot where your umbilical cord was attached before you were born. That cord was your lifeline in the womb, and once it was no longer needed, the place where it connected healed into the little dimple or bump you have today.
Your First Lifeline
Before birth, a baby can't eat or breathe on its own. Instead, it relies on the umbilical cord, which connects the baby to the placenta. The placenta passes nutrients and oxygen from the mother's blood to the baby without the two blood supplies directly mixing.
In humans, the cord normally holds two arteries and one vein, cushioned in a protective gel called Wharton's jelly. The vein carries oxygen-rich, nutrient-rich blood to the baby. The arteries carry used blood back to the placenta. The cord forms by about the fifth week of development, and through most of pregnancy it's roughly as long as the baby measured from head to bottom.
What Happens After Birth
Once a baby is born, the cord isn't needed anymore. Left alone, it naturally closes off shortly after birth as the jelly inside swells and collapses in the cooler air and the blood vessels tighten. Doctors or midwives clamp it and then cut it.
Here's a comforting detail: cutting the cord doesn't hurt the baby, because the cord has no nerves. It's surprisingly tough, though, a bit like thick sinew, so it takes a sharp instrument. A small stump is left behind, and it dries up and drops off by the time the baby is about three weeks old. If it hasn't, that's a reason to check in with the baby's doctor.
Innies, Outies, and Everything in Between
Because it's a scar, every belly button is unique. Doctors have even sorted them into types. An innie is any navel that dips inward. An outie is one where the scar pokes out past the surrounding skin. Within those groups are round, oval, vertical, T-shaped, and even rare swirly ones.
An outie is not a health problem in itself, though it's sometimes mistaken for a type of hernia, which is a different thing entirely. A belly button's shape can shift over time with changes in weight and exercise. A sudden, unexpected change is worth mentioning, so talk to your doctor.
The belly button is also handy for doctors in another way. Its position is fairly consistent from person to person, so it's used as a landmark to divide the abdomen into four sections.
We're Not the Only Ones
Humans aren't special here. All placental mammals have a navel, from dogs to whales, though it's usually much easier to spot on us. Animals that hatch from eggs, like birds, can have one too, but it looks more like a thin line. Scientists have even found a fossil of a small dinosaur called Psittacosaurus preserved with a navel.
So the next time you notice your belly button, give it a little respect. It's a permanent souvenir of the months you spent growing before anyone ever met you, and nobody else in the world has one quite like it.
