The navel (clinically known as the umbilicus, colloquially known as the belly button, umbilical dip or tummy button) is a scar on the abdomen at the attachment site of the umbilical cord. All placentalmammals have a navel, and it is quite conspicuous in humans. Other animals' navels tend to be smoother and flatter, often nothing more than a thin line, and are often obscured by fur.[unreliable medical source?]
The umbilicus is a prominent mark on the abdomen, with its position being relatively consistent amongst humans. The skin around the waist at the level of the umbilicus is supplied by the tenth thoracic spinal nerve (T10 dermatome). The umbilicus itself typically lies at a vertical level corresponding to the junction between the L3 and L4 vertebrae, with a normal variation among people between the L3 and L5 vertebrae. The umbilicus forms a visible depression on the skin of the abdomen, and the underlying abdominal muscle layers also present a concavity; thinness at this point contributes to a relative structural weakness, making it susceptible to hernia. During pregnancy, the uterus presses the navel of the pregnant woman outward; it usually retracts again after birth.
In humans, the navel scar can appear as a depression (often referred to colloquially as an "innie") or as a protrusion ("outie"). About 90% of humans have innies. The occurrence of an "outie" navel is caused by the extra scar tissue left from the umbilical cord[unreliable medical source?] or from umbilical hernias, although the latter does not always cause an "outie" to develop. Frequently separated into just those two categories, navels vary quite widely among people in terms of size, shape, depth, length, and overall appearance.
The navel can be involved in umbilical sinus or fistula, which in rare cases can lead to menstrual or fecal discharge from the navel. Menstrual discharge from the umbilicus is associated with umbilical endometriosis, a rare disorder.
There are many customs, fashion and taboos associated with the human navel in the human social context. These have varied in ideas and trends across regions and throughout history. Social mores about the navel in clothing and human social traditions has been given diverse narratives and significance across human social world.
^Bagade, Pallavi V; Guirguis, Mamdouh M (2009). "Menstruating from the umbilicus as a rare case of primary umbilical endometriosis: a case report". Journal of Medical Case Reports3 (1): 9326. doi:10.1186/1752-1947-3-9326. ISSN1752-1947.