Linea nigra is a hyperpigmented linear patch that extends from the pubis to the umbilicus. It is most commonly seen in pregnant individuals and is thought to be a result of increased sex hormone levels. In the neonate, linea nigra is attributed to maternal and placental hormones that result in a "mini puberty." It is more common in girls than boys and is more common in infants with darker skin colors. It is a normal variant and should not cause any concern if there are no associated ambiguous genitalia.
ICD10CM: L81.8 – Other specified disorders of pigmentation