Recently, three infants and toddlers in Wuhan were suspected of having abnormal physical development caused by eating formula milk powder containing “estrogen”. This has attracted a lot of attention from the community, with media coverage and panic among the parents of the children. In fact, it is not necessary. Milk is a special food produced by mammals to nurse their newborn cubs. It contains all the nutrients needed for the growth and development of the cubs and is known as the closest thing to perfect food. The characteristics of the milk of various animals are determined by their species and genetics, but they are also subject to changes due to acquired environmental factors. Milk is an organic substance with a very complex composition, and studies to date have proven that there are at least hundreds of chemical components in cow’s milk. In addition to what we already know: fats, proteins, carbohydrates, minerals, vitamins, there are also enzymes, organic acids, gases, cellular components, inorganic trace components, organic trace components, hormones, drug residues, etc. Estrogens are part of the hormonal substances in breast. In endocrinology, the steroid hormones estrogen and progesterone are collectively called estrogens, of which estrogen mainly includes three kinds of estrogen, estradiol and estriol. The steroid hormones in mammalian milk are mainly testosterone, estrogen and progesterone and their precursors and intermediates in the biosynthesis process, which are important for the development of young offspring and are called “growth factors” in many literatures. There are various free and bound forms of estradiol, estrone and estriol in milk. There are two forms of estradiol: 17β-estradiol and 17a-estradiol. The presence of estrogens in cow’s milk and the variation of their content reflect the physiological characteristics of pregnant cows. Their pattern of variation in cow’s milk is generally positively correlated with serum levels, and they enter milk through the blood-milk barrier in the circulation or can be partially synthesized by the mammary gland. The concentration of estradiol in plasma and milk is similar, but the concentration of estrone is four times higher than that in plasma. According to the literature, colostrum has the highest estrogen content, which is 10-20 times higher than that of regular milk. The concentrations of estrogens in human colostrum are: estrone 4-5 ng/mL, estradiol 0.54-5 ng/mL, and estriol 4-5 ng/mL, totaling 4-5 times that of bovine colostrum. The ratio of estrogenic activity in human colostrum to bovine colostrum is about 5:3. After 5 days of delivery, the estrogen content of the milk decreases rapidly and becomes normal milk. In human colostrum, estrone 22-41 pg/mL, estradiol n.d. (cannot be picked up)/mL, estriol 3.4-345 pg/mL; in bovine colostrum, estrone 12.7-31.1 pg/mL, estradiol 24.8-41.1 pg/mL, estriol 15 23.6 pg/mL. Estrone is a potent growth-inducing hormone in bovine milk, mainly in the form of fatty acid esters. It has been reported that it exhibits growth-promoting effects in experimental animals at natural concentrations in cow’s milk. The concentration of estrogen in cow’s milk is just right, and its intake can demonstrate physiological effects in suckling calves. The growth-promoting effects in infants and young children are well established, but it remains to be determined to what extent these effects are controlled by the presence of estrogens, since cow’s milk is a high-quality nutrient-rich, energy-concentrated natural food. Estrone has a low affinity for estrogen receptors and generally has no direct estrogenic effect. Estrogens will be rapidly bound and excreted after ingestion, and it is difficult for these estrogens ingested as food to have the opportunity to act on target tissues. Some studies have reported that estrogens in cow’s milk and its products are associated with the reproductive system and endocrine in those who ingest them, but the results are contradictory. A 2-generation reproduction test conducted by some scientists studied the effects of estrogen-like substances in cow’s milk on the reproductive system. The study showed that female rats consumed an average of about 20 ml of milk per day, and about 8000 pg of estrogen per day entered the female rats, but no significant effects on the ovaries and uterus were found; male rats consumed milk in large quantities for a long period of time (equivalent to 38 years of human life), and no significant effects on reproductive organs were found. Foreign scientists conducted research on the effect of milk on the reproductive function of the parental offspring of male and female rats and found that milk did not significantly damage the fertility, reproductive capacity and development of reproductive organs in both generations, and that it promoted the growth of rats under the premise of balanced nutrition. Processing has an effect on the estrogens in milk. The total amount of estrogens in most dairy products obtained after processing is lower than in their corresponding raw milk. Because estrogens are predominantly distributed in fat, defatting substantially reduces the free estrogen content of dairy products, typically removing 2/3. both free and acylated estrogens are tolerated by microbial processing. Estrogen conjugates remain stable during repeated freeze-thaw processes, but heat treatment has a significant effect on them, with common spray drying processes causing approximately 13-15% loss. There is a wide variety of estrogens in the daily environment with varying degrees of interaction, and the effects on human health of people exposed to various environmental estrogen-like substances (including estrogens in milk) are the result of the combined effects of these compounds. American pathologists believe that at very low concentrations, the result of the action of such environmental estrogens (which are substances present in the environment that have estrogen-like effects on human endocrine function and act on the body primarily through water, air, and food) is zero. At present, CAC, EC, and FDA of the U.S. have stipulated the certification, packaging, labeling and testing test methods for milk production, but there is no clear regulation on estrogen in milk. In our country, the safety management of milk and related research are mostly focused on microbial indicators, heavy metal indicators, pesticide and antibiotic residue indicators, etc., but there is less research on the safety of hormones in milk. There is no direct evidence to confirm that estrogen in milk is harmful to human body. There is no need for some consumers to worry and panic about the presence of estrogen in milk. First of all, dairies and processing plants do not add estrogen. The reason is that the addition of banned substances to products is driven by interest, one is the expectation of gaining economic benefits and the other is to make the best of a bad situation. The addition of “estrogen” not only does not achieve this purpose, but also increases the cost. Therefore, the possibility of artificial addition can be basically ruled out. If artificial addition is ruled out, then the milk produced by cows under normal feeding conditions should be within a normal range of estrogen content. According to scientists’ research results, formula milk powder with estrogen content within the normal range should not cause harm to consumers.