The darkening of the breasts when pregnant may be a normal physiological condition, or it may be caused by pathological factors, such as violent extrusion, melanoma, and so on. 1. Physiological factors: estrogen and progesterone in a woman’s body will slowly rise during pregnancy, thus causing darkening of breast pigmentation. 2. Pathological factors: (1) Violent squeezing: hard squeezing of the breasts will cause a stressful reaction of the skin, leading to an increase in melanin secretion, and the color of the breasts will become darker and darker. (2) Melanoma: Repeated spotting, freezing, chemicals and other factors can lead to the formation of melanoma, which can lead to darkening of the breasts during pregnancy. If the symptom of darkening of breasts during pregnancy persists in the clinic, it is recommended to consult a doctor in time, under the guidance of the doctor in order to clarify the specific cause of the disease and give targeted treatment.