The linea nigra, Latin for “black line,” is a common physiological change that occurs during pregnancy. This hyperpigmented line runs vertically down the midline of the abdomen, stretching from the pubic bone toward the navel, and sometimes extending up to the rib cage. It is a harmless and temporary skin change that affects up to 80% of pregnant women, particularly those with naturally darker complexions.
Timing of Appearance
The darkening of the abdominal line typically becomes noticeable during the second trimester of pregnancy. While the timing can vary significantly among individuals, most people observe the linea nigra forming around 20 to 22 weeks.
The line itself is the darkening of a pre-existing band of connective tissue known as the linea alba, or “white line,” which is usually colorless and virtually invisible before pregnancy. Hormonal shifts cause this faint line to become pigmented and visible. In rare cases, some individuals may notice a subtle darkening as early as the first trimester.
The Hormonal Mechanism
The biological cause of the linea nigra is a temporary increase in the production of melanin, the natural pigment that gives skin its color. This rise in melanin is directly stimulated by the high levels of pregnancy hormones circulating in the body.
Specifically, elevated concentrations of estrogen and progesterone act on the skin’s melanocytes, the cells responsible for producing pigment. These hormones stimulate the melanocytes to increase their output. The placenta is also thought to contribute by producing bioactive compounds that upregulate melanogenic enzymes.
This mechanism explains why hyperpigmentation is not limited to the abdomen. The same hormonal stimulation often causes other areas to darken, such as the areolas, nipples, and sometimes the face, a condition known as melasma.
Postpartum Fading
Because the appearance of the linea nigra is entirely driven by elevated pregnancy hormones, the line begins to fade as hormone levels normalize after childbirth. The process is gradual.
The dark line will typically start to lighten and may disappear completely within several months after delivery. For some, the line may take up to a year to fully resolve, and a faint shadow may persist permanently. It is also common for the linea nigra to reappear, sometimes earlier and darker, in subsequent pregnancies.
Safety and Management
The linea nigra is a benign cosmetic change that poses no risk to the health of the mother or the developing baby. Since sun exposure can intensify the pigmentation, basic sun protection is the primary form of management to minimize its darkness. Covering the abdomen or applying a broad-spectrum sunscreen when outdoors helps prevent the line from becoming more prominent. Bleaching creams or skin-lightening products are not advised, as they often contain ingredients like hydroquinone that are not proven safe for use during pregnancy or breastfeeding.