The causes of nipple darkening are mainly divided into the following cases: First, due to growth and development, female organs gradually mature, the body’s estrogen secretion stimulates the nipple and areola, resulting in pigmentation color deepening, belongs to the normal physiological changes. Second, the number of sexual life, too frequent, resulting in the nipples in a long-term congestion, hardened state, pigmentation color darkening. Thirdly, after pregnancy, the glands on the areola secrete vigorously, and the secretion of estrogen in the body increases to stimulate the nipples and also prepare for lactation, and the color deepens. Fourthly, repeated sucking stimulates the nipple and areola resulting in darkening of pigmentation, such as the birth of a second child. Fifth, repeated squeezing and touching the nipple, such as violent squeezing, traumatic collision or repeated rubbing of clothing, the skin is stimulated by stress reactions to darken the color. Sixth, genetic factors lead to darker nipples. Seventh, endocrine disorders, the body’s hormone secretion imbalance, such as estrogen or lactogen overproduction. Eighth, male nipples are darker due to external forces such as sunlight exposure or repeated friction.