Your belly button is your very first scar, left over from the umbilical cord and marking the spot where your cord was attached before you were born. Another name for the belly button is the navel, and doctors call it the umbilicus. Before birth the cord is a lifeline that connects a baby to the placenta. A baby in the womb does not eat or breathe air, so food and air reach the baby through the umbilical cord, and blood rich in oxygen and nutrients flows through it from the placenta to the baby so the baby can grow. The cord is long and thin, about 55 to 60 centimeters, which is about 22 inches, and only 1 to 2 centimeters thick.

The cord is twisted like a rope, with the two arteries winding in a spiral around the vein, and the whole bundle is wrapped in a thin, tube-like sheath made by the amnion, the bag that holds the baby. Inside the sheath the vessels are packed in Wharton's jelly, a soft, jelly-like cushion that works like a built-in shock absorber, and the jelly cushions the cord's vessels against being squeezed, twisted or bent when the baby kicks and turns. It is a gel with a rich matrix that surrounds the two arteries and the vein and resists squeezing and twisting, so blood keeps flowing.

Blood moves in both directions along the cord, which also carries waste away from the baby. The two arteries carry oxygen-poor blood from the baby back to the placenta, where the waste is taken out of it, and the cleaned blood returns to the baby along the vein. In the womb the baby does not breathe air, so the placenta does the work of the lungs, and oxygen comes in through the cord. The baby's body also has shortcuts. A shortcut called the ductus venosus lets a large share of the blood from the cord skip the liver and flow straight toward the heart, and a small opening in the heart, the foramen ovale, lets blood skip the lungs.

At birth the first breaths fill the lungs with air, and blood then starts to flow to the lungs instead of taking fetal shortcuts, a change that begins within seconds. The baby breathes air with its lungs, so the cord is not needed for oxygen anymore, and the foramen ovale closes, usually sealing within about 3 months and leaving a dent called the fossa ovalis. Another shortcut, the ductus arteriosus, is a short blood vessel that sends blood past the lungs, and breathing makes its muscle tighten for good within 10 to 15 hours, so that it becomes a fibrous string, the ligamentum arteriosum. The ductus venosus closes after birth and turns into a fibrous string called the ligamentum venosum.

After birth the cord's blood vessels inside the body close up, and the belly button holds the sealed-off ends of the one vein and two arteries. The umbilical vein shrinks into a tough fibrous string called the round ligament of the liver, also known as the ligamentum teres, and it stays there for life as a leftover of the cord. The two umbilical arteries shrink to fibrous strings too, with their far ends becoming the medial umbilical ligaments, which stay in the belly for life, while the near ends stay as working arteries.

Right after birth, the cord is clamped, which means pinched shut, and then cut. Before the 1960s it was not unusual to wait five minutes or more to cut the cord, and then, for reasons that are unclear, doctors began clamping and cutting almost right away. The value of that quick cut was never shown, and doctors now study timing again. As of November 2026, the group of obstetricians in the United States called ACOG advises waiting at least 30 to 60 seconds before clamping the cord of a healthy baby, in guidance from 2016 and later. Waiting lets extra blood move from the placenta to a full-term baby, giving the baby more iron stored in the body in the first months of life.

For babies born too early, waiting has been linked to a lower risk of needing blood transfusions, of anemia, and of bleeding in the brain. Waiting may slightly raise the chance of newborn jaundice, a yellow tint to the skin that doctors watch for and can treat, and hospitals that delay clamping are set up to monitor for it. Doctors do not wait when the baby needs help right away, for example if the baby has trouble breathing and needs emergency care. What the cut leaves behind is a short piece of cord, the stump, on the baby's belly.

At first the stump is soft, moist and bluish white or yellowish green, and then it turns yellow, then brown or black, a bit like a scab. Dry, dark and crusty is normal for a stump that is healing. The stump dries up and falls off, usually within one to three weeks after birth, though some take a bit longer, and it leaves behind the dent we call a navel. It will come off by itself, even if it looks like it is barely hanging on, so grown-ups are told not to pull on it. To keep it dry, they fold the top of the baby's diaper down below the stump, and they do not put rubbing alcohol, lotion or anything else on it.

If the stump gets dirty, grown-ups rinse it with plain water and a soft cloth, then pat it dry, and a baby gets sponge baths instead of a bath in a tub while the stump is still on. A few drops of blood on the diaper around the time the stump falls off are normal. If the cord actively bleeds, grown-ups call the baby's doctor right away. Signs that a stump may be infected include a foul smell, yellowish fluid, red skin around the base and crying when the area is touched. Infections are rare, but a doctor should see the baby quickly, and a kid who sees a stump that is red, swollen, smelly or bleeding should tell a grown-up. A baby whose stump has not fallen off by about 3 weeks of age should also see a doctor.

An umbilical granuloma is a small, moist, pink or red lump of extra scar tissue that can form on a baby's belly button after the stump falls off. It is usually harmless and often goes away in about a week. Many babies are born with an umbilical hernia, a bulge at the belly button that forms when part of the intestine pushes through a weak spot in the belly muscles near the belly button. Most umbilical hernias in children go away on their own, usually by about age 5, and a baby's hernia most often heals in the first 12 to 18 months of life. A child's hernia usually needs treatment only if it is very big or does not go away, and one larger than about 2 centimeters is more likely to need surgery. Taping a coin over a belly button does not fix a hernia or change an outie.

An innie is a little dent in the belly, and an outie sticks out. An innie sinks in, with the skin around it folding inward, while an outie is often caused by a little extra scar tissue. Most belly buttons are innies, and outies are less common. No one knows exactly why some belly buttons are outies, though it may depend on how the cord area heals and on how much space lies between the skin and the belly wall, which changes how much of the stump stays visible or tucks away. Some outies are caused by an umbilical hernia or an umbilical granuloma, and both are generally harmless, but a doctor should look at them.

Scientists have studied the navel as a home for bacteria. A study that used swabs from 60 volunteers found 2,368 kinds of bacteria in their belly buttons, with about 67 kinds on average in each one, though some had as few as 29 and some as many as 107, and only about 6 to 8 kinds were common to most people in the study. Most kinds were rare, so scientists compared belly buttons to rainforests, and doctors also use the navel as a reference point on the belly, for example when examining a patient. They have names for its parts: a hump in the middle called the mamelon, a dense scar called the cicatrix, a raised skin edge called the cushion, and folds called furrows.

Most of what makes a navel is dense scar tissue, and the cicatrix is a fusion of several fibrous structures, including the round ligament of the liver, the median umbilical ligament and two medial umbilical ligaments. The umbilicus is a fibrous scar that holds the closed-off openings of the three umbilical vessels, and after birth the cord comes away, so that the navel is what remains, your very first scar.

Words to know

• granuloma: extra scar lump
• amnion: baby's water bag
• fibrous: stringy
• jaundice: yellow tint
• cicatrix: dense scar