From the Guidelines
Linea nigra is caused by increased melanin production stimulated by pregnancy hormones, resulting in a dark vertical line on the abdomen. This condition is a harmless skin change that affects up to 75% of pregnant women, typically appearing around the second trimester and fading within a few months after delivery 1. The exact mechanism is not fully discussed in the provided evidence, but it is known that the line is actually present in everyone, called the linea alba or "white line" when not darkened, and becomes visible during pregnancy due to hyperpigmentation. Some key points to consider about linea nigra include:
- It is a normal physiological change that does not require treatment
- The intensity of the line may be more pronounced in women with darker skin tones
- Protecting the abdomen from sun exposure can help prevent the line from darkening further during pregnancy
- While primarily associated with pregnancy, it can rarely appear in non-pregnant individuals due to hormonal conditions or medications. It's worth noting that the provided evidence primarily discusses the management of cutaneous melanoma during pregnancy, but does not directly address the cause of linea nigra, however, the relationship between hormonal changes and skin pigmentation is well established 1.
From the Research
Causes of Linea Nigra
- The development of linea nigra has been postulated to be caused by elevated estrogen, progesterone, and/or melanocyte-stimulating hormone levels during gestation 2.
- Hormonal and immunological changes associated with pregnancy may also contribute to the development of linea nigra 3.
- Endocrinological changes during pregnancy can lead to skin hyperpigmentation, including linea nigra 4.
- In men, linea nigra has been found to be more common in those with benign prostate hyperplasia or prostate cancer, suggesting a possible hormonal link 5.
- Physiologic pigmentary changes, including linea nigra, can occur during pregnancy due to the new hormonal milieu 6.
Associated Factors
- Linea nigra is frequently observed as a physiologic change associated with pregnancy, with an incidence ranging from 32% to 92% in pregnant women 2.
- The skin darkening often partially or completely resolves spontaneously after delivery 2.
- Linea nigra is not restricted to gestational females and has also been noted in newborns, children, and men 2, 5.
- The presence of linea nigra alone cannot be used to differentiate between benign prostate hyperplasia and prostate cancer in men 5.