Look at your belly button. It is a scar. It is left over from the umbilical cord. Your belly button is the spot where your cord was attached before you were born. The cord is a lifeline that connects a baby to the placenta before birth. So you can find the place where the lifeline once joined you, right in the middle of your body.

Before birth, food and air reach a baby through the cord. A baby does not eat or breathe air in the womb. Through the cord, blood rich in oxygen and nutrients flows from the placenta so the baby can grow. After birth, a baby breathes air with its lungs, so the cord is not needed for oxygen anymore.

Inside the cord are three blood vessels: two arteries and one vein. The vein brings in blood with oxygen and food. The arteries carry used blood and waste back to the placenta. The cord is also twisted like a rope. The two arteries wind in a spiral around the vein.

Doctors often wait a short time before clamping and cutting the cord. In the United States, a group of doctors called ACOG advises waiting at least 30 to 60 seconds for healthy babies, as of November 2026. Then the cord is clamped, which means pinched shut, and cut. A short stump is left on the belly.

The stump changes color as it dries. At first it is soft, moist and bluish white or yellowish green. Then it turns yellow, then brown or black before it falls off. Most stumps fall off one to three weeks after birth, though some take a bit longer.

While the stump is healing, it should be kept clean and dry. Adults are told not to pull or tug at it, even if it looks like it is barely hanging on, because it will come off by itself. They do not need to put alcohol, lotion or anything else on it. If it gets dirty, they rinse it with plain water. Keeping it clean and dry is the whole job.

Red or swollen skin around the base of the cord is a sign of a stump infection. If a kid ever sees a stump that is red, swollen, smelly or bleeding, the kid should tell an adult. A doctor should check it. If the stump has not fallen off by about 3 weeks, a doctor should see it. If the cord actively bleeds, adults call the doctor right away.

Most belly buttons are innies. Outies are less common. An innie sinks in, with the skin around it folding inward. An outie sticks out, often because of a little extra scar tissue. How a doctor cut or tied the cord does not decide which one you get. Nobody gets to choose an innie or an outie. It is mostly a matter of chance.

Many babies are born with a bulge at the belly button, called a hernia. It forms when part of the intestine pushes through a weak spot in the belly muscles near the belly button. A hernia usually heals by itself, most often in the first 12 to 18 months of life. Most hernias in children go away on their own, usually by about age 5, so the bulge is common, and it often goes away.

Most mammals have belly buttons, but you may not see them. On a dog or a cat the navel is a small flat scar that is hidden by fur. Chimpanzees and gorillas have ones that look a lot like ours. Monotremes, such as the platypus and echidna, are mammals that lay eggs. Their young hatch from eggs. Platypuses lay eggs, so they have no cord and no belly button.

Words to know

• umbilical: of the cord
• arteries: blood tubes
• hernia: a bulge
• placenta: cord's start
• stump: bit of cord