Darkening of breasts during pregnancy may be caused by bad habits, rising hormone levels and breast eczema. 1. Bad living habits: If you wear underwear that is too tight, or if you don’t wear underwear for a long time and rub it repeatedly, so that the nipple is stimulated, it may lead to darkening of the breasts during pregnancy. 2. Rising hormone levels: Due to the influence of hormone levels, progesterone levels and estrogen levels will gradually rise, which will be accompanied by deepening of breast color, darkening of nipples and enlargement of areola. 3. Breast eczema: This is a non-specific allergic inflammation that occurs in the skin of the nipple and areola, and if there is breast eczema on top of the breast, it may also lead to the deepening of the local skin color to black. If there is a darkening of the breasts during pregnancy, it is recommended to go to a regular hospital, eat more fresh fruits and vegetables, wear cotton thread underwear to avoid friction and stimulation.