Darkening of the nipples is related to pregnancy, endocrine disorders, trauma, and age. When women of childbearing age have darkened nipples, they should consider it to be due to pregnancy. During pregnancy, the formation of the placenta secretes estrogen, which stimulates the development of the mammary glands. At the same time, progesterone is also secreted to stimulate the development of the mammary vesicles, when the breasts begin to enlarge and become engorged with blood, causing swelling and pain in the breast area. During pregnancy, the secretion of estrogen, progesterone and various hormones gradually increases, causing pigmentation that leads to darkening of the nipples. Traumatic nipple injuries caused by various factors tend to have local pigmentation when healing, resulting in dark nipples. The darkening of nipples is also related to age, as women’s nipples gradually become darker when they reach a certain age. As the body’s cells gradually age, the rapid secretion of estrogen combined with melanin deposits in the nipple tissue can cause the nipples to turn black.