Linea nigra
Linea nigra, denoted by its Latin translation "black line," colloquially known as the pregnancy line, manifests as a linear area of heightened pigmentation frequently observed on the abdominal region during pregnancy. Typically spanning approximately one centimeter (0.4 in) in width, this brownish streak extends vertically along the midline of the abdomen, spanning from the pubis to the umbilicus. Variably, it may traverse from the pubis to the upper abdominal region. For pregnant women, the emergence of linea nigra is attributed to an increased production of melanocyte-stimulating hormone by the placenta. This physiological phenomenon is concomitant with the occurrence of melasma and darkened nipples. Individuals with lighter skin pigmentation tend to exhibit this phenomenon less frequently in comparison to those possessing darker pigmentation. It is typical for the linea nigra to fade and dissipate within several months following childbirth. Although predominantly associated with pregnancy, it can manifest in both males and females of all ages. Beyond the gestational context, its prevalence is found to be uniformly elevated in both sexes during the ages of 11 to 15. This is potentially attributable to hormonal fluctuations characteristic of puberty. Subsequent to the age of 15, the prevalence of the linea nigra in both males and females declines. Particularly in postpubescent females, it often serves as an indicator of elevated benign estrogens. The prevalence of this phenomenon in both genders drops below 10% following the age of 30. Furthermore, its appearance may ensue subsequent to rapid weight gain over a short interval. It could also rarely serve as an indicator of underlying hormonal imbalances, genetic disorders, malignancy, inflammation, or even fungal infections. Additional images

See also
 Chadwick's sign
 Linea alba
 List of cutaneous conditions
 Perineal raphe

References

Pregnancy-related cutaneous conditions
Disturbances of human pigmentation
Medical signs
Human pregnancy
Pathology of pregnancy, childbirth and the puerperium