Hello, you are talking about breastfeeding. Human mammary glands are derived from ectoderm. In the second month of embryo development, 6 ~ 8 pairs of mammary primordia are formed on the "mammary gland line" from armpit to groin on the ventral side of embryo. Under normal circumstances, by the ninth week of embryonic development, except for a pair of breast primordia located between the fifth ribs in the chest area, they can be preserved and continue to develop, and the rest are degenerated and disappeared. If the remaining pair (or pairs) of mammary glands do not disappear, they will develop into redundant breasts or nipples after birth, which is attached breasts (multiple breasts or nipples). Most auxiliary breasts have only one pair, but single or multiple pairs can also appear. If there is nipple formation accompanied by glandular tissue under it, it is called complete breast attachment; If there are only nipples without breast parenchyma, or only bilateral symmetrical localized depressions or skin pigmentation without nipples, it is called breast imperfection. Don't panic when you find breast milk. If it belongs to incomplete breast attachment, it is usually insensitive and rarely has lesions; If it is a complete breast attachment, you should pay attention to observation and see a doctor in time if you find any abnormality.