Generality
Linea nigra is a dark skin mark that appears in the center of the abdomen, usually starting in the second trimester of pregnancy.
This phenomenon is physiological and quite common. The linea nigra depends, in fact, on the strong hormonal stimulation typical of pregnancy, which increases the production of melanin and causes a "hyperpigmentation of the skin.
This manifestation usually disappears within a few weeks of giving birth, completely spontaneously and without any treatment.
Note
During pregnancy, linea nigra may appear in some women, while in others it may not. This sign is more evident in dark-skinned mothers-to-be and can become more pronounced following exposure to sunlight.
In any case, the linea nigra is by no means an indicator of the evolution of pregnancy.
Features
The linea nigra is a vertical skin mark, of shades from brown to dark brown, and about one centimeter wide.
This hyperpigmentation extends along the center of the belly to the pubis, crossing the navel; in some women, however, this strip can reach the upper abdomen or the area under the breasts.
The position of the darker skin strip coincides with the linea alba. During pregnancy, in fact, this fibrotic structure, located in the median portion of the abdomen, can become hyperpigmented by the action of estrogen hormones, thus giving rise to the linea nigra. The latter generally appears in the vicinity of the fourth or fifth month of gestation, presenting itself as a very thin line, which slowly expands and gradually becomes darker. However, it cannot be ruled out that the linea nigra already manifests itself around the fourteenth week. or, on the contrary, it is never evident.
What is the linea alba?
The linea alba is located between the margins of the two rectus muscles and is formed by the aponeurosis of the external oblique muscle, the internal oblique muscle and the transverse muscle.
Causes
Linea nigra generally appears near the second trimester, due to the strong hormonal stimulation typical of pregnancy.
The increase in estrogen has, in particular, an effect on the melanocyte-stimulating hormone which is produced by the placenta.
The action of these hormones stimulates the production of melanin, making a brown line emerge from the pubis to the navel and, sometimes, to the lower part of the sternum. The linea nigra originates from the resulting hyperpigmentation phenomenon.
The increase in melanin production also affects other areas of the face and body, such as the sides of the nose, upper lip, cheeks and forehead (the so-called chloasma gravidarum), areolas, vulva and inner thighs. areas may become darker, as well as any scar tissue, freckles and nevi may appear more noticeable than before.
After childbirth, the linea nigra tends to lighten, until it disappears completely within a few months, although in some women the return to normal pigmentation can take up to a year.
