An umbilical hernia happens when tissue pushes through a weak spot in the abdominal wall at or near the belly button. In adults, about 90% of these hernias are acquired, meaning they develop over time rather than being present from birth. The underlying cause is always the same basic combination: a structural weakness in the abdominal wall plus enough pressure from inside the abdomen to force tissue through that weak point.
How the Abdominal Wall Gives Way
Your belly button is a natural weak spot. It’s where the umbilical cord once passed through, and the tissue there never becomes as strong as the surrounding muscle and connective tissue. In most people, this isn’t a problem. But when the muscle fibers of the abdominal wall stretch apart or the tough connective tissue sheets (called aponeuroses) weaken, a gap can open up. Abdominal contents, usually a small pad of fat or a loop of intestine, can then bulge through that gap.
You might first notice it as a soft lump near your belly button that appears when you cough, strain, or change posture, then flattens when you lie down or press on it gently. That’s the hallmark of a reducible hernia, where the tissue slides back and forth through the opening.
Causes in Infants
In babies, umbilical hernias are congenital. After the umbilical cord is cut, the ring of tissue it passed through is supposed to close on its own as the baby grows. When that ring doesn’t fully seal, a small hernia forms. This is common in newborns and usually not dangerous. Most pediatric hospitals consider it safe to simply watch and wait until age 4 to 5, because the majority of these hernias close without treatment. If the opening hasn’t sealed by age 5, surgery is typically recommended.
Certain genetic conditions raise the likelihood that this ring won’t close on schedule, including Down syndrome and Beckwith-Wiedemann syndrome.
What Drives Adult Umbilical Hernias
For adults, the root cause is chronic or repeated increases in pressure inside the abdomen. That pressure pushes against an already vulnerable spot, and over time the tissue gives way. The most common drivers include:
- Obesity: Excess abdominal fat both increases internal pressure and physically separates muscle fibers, weakening the wall from two directions at once.
- Multiple pregnancies: Each pregnancy stretches the abdominal muscles further. Umbilical hernias are more common in women partly for this reason.
- Chronic constipation: Repeated straining during bowel movements creates surges of abdominal pressure over months or years.
- Heavy lifting: Regular heavy exertion, especially with poor core bracing, stresses the abdominal wall repeatedly.
- Fluid buildup in the abdomen (ascites): Often linked to liver disease, this creates constant, sometimes extreme pressure from within.
- Previous abdominal surgery: Scar tissue at or near the belly button can leave the area structurally compromised.
- Long-term peritoneal dialysis: The repeated filling and draining of fluid in the abdomen for kidney failure treatment increases pressure over time.
Poor nutrition also plays a role. When the body lacks adequate protein, the connective tissue that holds the abdominal wall together can weaken, making herniation more likely even at lower levels of pressure.
Pregnancy as a Specific Risk Factor
Pregnancy deserves its own discussion because it combines several hernia-causing forces at once. The growing uterus pushes intestinal loops upward and backward, physically rearranging the abdominal contents and increasing pressure on the front wall. At the same time, the body produces a hormone called relaxin, which loosens ligaments and breaks down collagen. That hormonal shift softens connective tissue throughout the body, including the tissue around the belly button.
On top of that, many pregnant women develop diastasis recti, a separation of the two bands of abdominal muscle that run down the center of the belly. This separation can persist after delivery and significantly raises the risk of hernia. The reported incidence of umbilical hernia during pregnancy is about 0.08%, relatively low, but the combination of stretched muscles, hormonal tissue softening, and diastasis recti means the postpartum period is also a vulnerable time.
The Role of Liver Disease and Ascites
People with liver cirrhosis face an especially high risk. Ascites, the buildup of fluid in the abdominal cavity, is likely the single biggest contributing factor in this group. The fluid creates relentless inward pressure that can force abdominal contents through even a small defect at the belly button.
But the problem goes deeper than just pressure. Cirrhosis causes low levels of a key blood protein called albumin, and that protein deficiency weakens the abdominal wall muscles. Portal hypertension, a complication of advanced liver disease, can also cause veins around the belly button to swell and dilate, further destabilizing the area. In severe cases with tense ascites, the pressure can actually cause the skin overlying the hernia to break down, a dangerous complication that can lead to infection.
Connective Tissue and Genetic Factors
Some people are simply more vulnerable because of how their connective tissue is built. Connective tissue disorders, conditions where the body produces weaker-than-normal collagen or structural proteins, make the abdominal wall less resilient to normal wear and strain. Ethnic background also appears to play a role in susceptibility, though the exact genetic mechanisms are still being clarified. Metabolic syndrome, the cluster of conditions including high blood pressure, high blood sugar, and excess abdominal fat, independently raises risk as well.
When a Hernia Becomes Dangerous
Most umbilical hernias are not emergencies, but they can become one. The main danger is incarceration, which means the tissue that has pushed through the opening gets stuck and can’t slide back in. You might feel a firm, painful lump at the belly button that won’t flatten when you lie down. Nausea and vomiting often follow.
If the trapped tissue loses its blood supply, the hernia is considered strangulated. This is a surgical emergency. The warning signs are severe, worsening pain at the hernia site, skin over the bulge that turns red or dark, fever, and vomiting. Strangulation can lead to tissue death within hours, so sudden onset of these symptoms warrants immediate medical attention. Adult umbilical hernias carry a higher risk of incarceration and strangulation than the same hernias in children, which is one reason doctors are more likely to recommend repair in adults even when the hernia seems small.