Everyone has one, but you may not know much about it. Here biologist Sarah Leupenwho teaches human and animal physiology explains the ins and outs of umbilical cords.
1. Why do I even have a belly button?
Your navel or navel – clinically, your navel – is the permanent scar left from where your umbilical cord connected your circulatory system when you were a fetus to the placenta. Fetuses don’t breathe, eat, or excrete waste, so the placenta provides an exchange site for the mother to deliver oxygen and nutrients from her bloodstream to the fetus, as well as collect waste to remove from her body.
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After the baby is born, the doctor or other attendant cuts the umbilical cord and clamps off the stump, which then dries and falls off in about a week, leaving the connection point – your navel.
If the umbilical cord is not cut, as is customary in some times and places and becomes fashionable in others, it will close in about an hour and detach naturally a few days after birth. Some healthcare providers are concerned that this “lotus birth” can be a risk of infection as the umbilical cord remains attached to the placenta, which is dead tissue once it is out of the mother’s body.
2. If it’s a scar, why won’t it disappear over time?
If you only injure the outer layers of your skin, such as with a cut or burn, the scar will quickly disappear completely, especially in young people. And newborns are very young people. But unlike in those situations, the navel includes more layers of tissue — not just the skin but the connective tissue underneath — so it makes sense that it doesn’t just blend in with the rest of your abdominal wall once it’s healed.
What about some pretty complicated surgeries that don’t leave any scars? Doctors perform many surgeries in ways that deliberately avoid scarring, which is not the natural way. One way to minimize scarring in surgery is this existing scar. Surgeons may use the navel as an incision site for pneumonia removing your appendix or gall bladder or before weight loss surgery.
But if you don’t like the look of your umbilical scar, plastic surgery to change the look, called umbilical cord plastic, is possible. People sometimes choose this cosmetic option after pregnancy or piercing removal, or simply to turn an “outie” into an “innie.”
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3. But why do some people actually have outings?
The appearance of your belly button is not related to the location of the clamp or where your doctor cut the umbilical cord.
Outies are just one example of that normal human variation, as some people have curly hair or dimples. When the end of the umbilical cord remnant protrudes beyond the skin around it, you have an outing; about 10% of people have it. Any concave navel is called an “innie” and a convex one an “outie”.
Sometimes outings can be caused by an umbilical hernia in the baby or some other medical problem, but most of it is simply due to what your genes coded for. You may also have a temporary break in late pregnancy, when abdominal pressure from the growing fetus stretches and possibly pushes your navel out.
4. How deep does it go?
You can probably easily gauge the depth of your own belly button – there are no hidden recesses there. What’s underneath is the same as what’s under the skin of the rest of your abdomen: your abdominal muscles, to which the navel is attached by a short umbilical cord, and the peritoneum, the membrane that lines the abdominal cavity. Below that are your intestines – that is, your intestines and other abdominal organs. If you keep following this imaginary journey back, you’ll get to your spine – the navel is usually aligned between the third and fourth lumbar vertebrae (L3 and L4).
5. Do other animals have navels?
Because the navel is a scar from where the umbilical cord connected the fetus to the placenta, all placental mammals have them. That includes all mammals except marsupials (such as kangaroos and possums) and monotremes (such as platypuses and echidnas).
Your cat, dog, or guinea pig does have a belly button, but because it’s a flatter scar than a person’s rather than a hollow scar, and because it’s covered in fur, you may have missed it.
6. Is there anything besides fluff in it?
Like any hollow surface, if you have an innie it probably collects bits of debris from time to time. Your belly button also has a microbiota, just like the rest of your skin. Because it is quite protected from soap and abrasion, one more stable and diverse bacterial community lives in your navel than elsewhere on your skin surface.
The innovative Belly Button Biodiversity Project at North Carolina State University has revealed a lot about these little friends. The researchers found more than 2,000 species of bacteria in the first 60 umbilical cords they examined.
It seems that most people have a set of eight common navel bacteria, but the project is constantly discovering new ones.
7. Why are some people disgusted by their belly buttons?
There hasn’t really been much research into why some people find navels repulsive.
It can overlap with omphalophobia, the fear of umbilical cords and touching them. There is no specific treatment outside of therapy or anti-anxiety medications that a doctor can prescribe for another phobia.
Whatever your feelings about umbilical cords, they are harmless. Plus, they’re part of your evolutionary legacy as mammals, the group of animals so invested in their offspring that they invented a way to deliver nutrients and oxygen, the mother’s bread and breath, directly to their developing young. Your belly button may be a reminder of that first life support care you received from another person before you were even born.
