The belly button, medically known as the umbilicus or navel, is present in all placental mammals. It is not an organ or a gland, but rather a unique scar that marks the point where the umbilical cord once connected a developing fetus to the placenta. The navel provides a permanent record of the body’s transition from dependence on the mother to independent physiological life.
The Essential Function During Fetal Development
The function of the navel’s precursor is to facilitate life support during the nine months of gestation. The umbilical cord, which attaches the fetus to the placenta, acts as a conduit for gas exchange and nutrient transfer. Within the cord are three distinct vessels essential for fetal survival.
One umbilical vein carries oxygen-rich and nutrient-dense blood directly from the placenta to the developing fetus. Conversely, two umbilical arteries transport deoxygenated blood and metabolic waste products away from the fetus and back to the placenta for disposal into the maternal bloodstream. This structure allows the placenta to function as the fetus’s temporary lungs, kidneys, and gastrointestinal tract.
Why It Is Now Biologically Inert
The moment a newborn begins breathing and its circulatory system adjusts to independent life, the cord’s utility immediately ceases. After the umbilical cord is clamped and severed, the remaining stump typically dries up and falls off within one to three weeks, creating the characteristic scar tissue known as the navel.
The internal blood vessels that once extended into the body rapidly close off and atrophy. The single umbilical vein collapses and fibroses to become the round ligament of the liver. The two umbilical arteries seal shut and transform into the medial umbilical ligaments within the abdominal wall. Because all the internal structures associated with the navel have closed and become non-functional ligaments, the navel itself serves no active physiological purpose in an adult. It is merely a closed entry point and a biological relic of prenatal life.
Anatomy and Common Variations in Shape
The external appearance of the navel is a direct result of how the scar tissue forms after the umbilical stump detachment. Its final shape is largely determined by the amount of scar tissue present and the surrounding abdominal fat and muscle structure. Contrary to popular belief, the way a physician clamps or cuts the umbilical cord has no bearing on the final shape.
Most individuals, approximately 90 percent, develop an “innie” navel, which is a depression or indentation in the abdomen. An “outie” navel, which protrudes outward, is often the result of an umbilical granuloma—extra tissue that forms as the stump heals—or a small, usually harmless umbilical hernia. The final cosmetic look of the navel is ultimately a matter of chance and the individual healing process.
Navel Hygiene and Health Concerns
The structure of the umbilicus, particularly the indented “innie” type, creates a warm, dark, and often moist environment that can trap debris. This crevice can easily accumulate skin oils, dead skin cells, sweat, and fabric lint, which can lead to odor and potential health issues if not cleaned. A 2012 study found over 2,300 different species of bacteria residing in the navels of a small sample population, highlighting the need for routine hygiene.
Cleaning the navel gently with mild soap and water during a regular bath or shower is typically sufficient to prevent the accumulation of debris and odor. Failure to maintain cleanliness can lead to mild bacterial or fungal infections, often presenting with redness, discharge, or pain.
Health Concerns
In infants, a condition called omphalitis is an infection of the navel stump that requires prompt medical attention, as untreated infections can rarely lead to serious complications. Umbilical hernias, where abdominal tissue pushes through a weak spot near the navel, are another common concern, especially in newborns or during periods of increased abdominal pressure like pregnancy.