Overview of the Hormones in Breast Milk (2023)

Breast milk contains more than just calories and nutrients. In fact, it's chock full of other ingredients, such as hormones. These hormones play a role in a baby's health and development. This is one of the many differences in the makeup of breast milk compared with formula.

Many of the hormones in breast milk have only recently been identified, and research is ongoing to determine what specifically these hormones and other components do for babies. It is believed that they offer significant health benefits, as research finds significant health advantages for breastfed babies.

Infant formula is, of course, a safe alternative to breast milk—and formula-fed babies also thrive. That said, formula does not contain the same makeup of hormones, antibodies, or enzymes. And, without all the necessary information, it's just not possible to try to recreate the precise hormone composition of breast milk in infant formula.

What Are Hormones?

Hormonesare chemicals that are released into the blood from different parts of the body. They carry messages to organs and tissues to tell them what the body needs and what to do.

Hormones can be found inblood,urine,saliva, and breast milk. Hormones have many jobs. They control reproduction, growth and development, metabolism, blood pressure, and other important body functions.

What's Inside Your Breast Milk?

Breast milk contains many hormones thatpass into it from your body. Some hormones are smaller with a simple structure so they can move more easily into breast milk. Other hormones are larger and may not pass into the breast milk well, if at all.

(Video) Breastfeeding hormones in play

The levels of the different hormones in breast milk do not remain constant. In fact, they fluctuate quite a bit, particularly in the postpartum period and once menstruation resumes. So, as time goes on, your breast milk will have more of some hormones and less of others.


Prolactin is the hormone responsible for the production of breast milk. Colostrum, the first breast milk, has high amounts of prolactin. Following the first few days of breastfeeding, the amount of prolactin goes down quickly. After that, the levels of prolactin in breast milk are about the same as the levels of prolactin in the blood.

Prolactin and Breastfeeding

Thyroid Hormones: TSH, T3, and T4

Thyroid hormones are madeby the thyroid gland. They perform many important functions, and they affect almost every system in the body. The most important function of the thyroid hormones is to control how the body breaks down food and turns it into energy.

This process is called metabolism. Thyroid hormones also regulate breathing, heart rate, digestion, and body temperature. And, they play a vital role in growth and development.

(Video) Physiology of Lactation Animation

Thyroxine (T4) levels in colostrum start out low, but they go up during the first week of breastfeeding. Thyroxine may help the intestines of a newborn develop and mature. During the first few months of life, breastfed babies have much higher levels of thyroxine in their bodies than formula-fed infants do.

Small amounts of triiodothyronine (T3) and thyroid-stimulating hormone (TSH) have also been identified in breast milk. It's believed that the thyroid hormones in breast milk help to protect a breastfed newborn from hypothyroidism. However, there isn't enough evidence available to confirm this theory.

Epidermal Growth Factor (EGF)

The epidermal growth factor stimulates cell growth. It is especially important for the development and maturation of the gastrointestinal (GI) tract, or digestive system, of newborns. EGF can be found in blood, saliva, amniotic fluid, and breast milk.

Colostrum contains high amounts of epidermal growth factor. The levels go down quickly after childbirth. But a parent with a very early preemie (between 23 and 27 weeks) will have much higher levels of EGF in their breast milk for the first month after delivery.

Having more EGF in early preterm breast milk is important because babies born at this stage have a greater chance of developing GI problems such as necrotizing enterocolitis (NEC). The higher levels of EGF may help to prevent this type of serious intestinal issue.

Other growth-promoting factors including human milk growth factors I, II, and III (HMGF), and insulin-like growth factor (IGF-I) have alsobeen identified in human breast milk.

(Video) What factors affect stress hormones in breast milk?


Endorphin hormones are the body's naturalpainkillers. The beta-endorphins found in breast milk are believed to help newborns deal with the stress of birth and adjust tolifeoutside of the womb. Interestingly, there are higher levels of beta-endorphins in the breast milk of people who have a typical vaginal delivery, those who have a premature baby, and those who do not get an epidural during childbirth.


Relaxin is a hormone that plays a big role in reproduction. Relaxin, as you may have guessed from the name, relaxes or loosens muscles, joints, and tendons. During childbirth, relaxin in the body works to help soften the cervix and loosen the pelvis to prepare for delivery. It may also have an effect on the growth of the milk-making tissue of the breasts.

Relaxin is present in early breast milk, and it continues to be seen in breast milk for weeks after childbirth. The importance ofrelaxinin breast milk is still unknown, butitsfunction may be related to the newborn's stomach and intestines. Since scientists do not fully understand all that relaxin does, research on this hormone continues.

Erythropoietin (EPO)

The production of red blood cells in the body is called erythropoiesis. Erythropoietin is a hormone that's made by the kidneys. It tells the body to make more red blood cells. This hormone passes into breast milk and may help to stimulate the production of red blood cells in the newborn.


Cortisol is often called the stress hormone. It's a steroid hormone that has many functions in the human body. In colostrum, cortisol is high, but the levels go down quicklyand stay at lower levels as breastfeeding continues. Studies show that people who are happy and have a positive breastfeeding experience have less cortisol in their breast milk.

The amount of cortisol in breast milk can affect the amount of secretory immunoglobulin A (sIgA). IgA is an important antibody that protects a baby from illness and disease. Higher levels of cortisol are associated with lower levels of sIgA. So, it appears that high levels of stress and cortisolcan interfere with the healthy immune-protecting properties of breast milk.

(Video) Breast anatomy and lactation | Reproductive system physiology | NCLEX-RN | Khan Academy

The scientific community is not sure exactly what impact cortisol in breast milk has, but they believe that it may:

  • Be involved in the growth of the baby's pancreas
  • Help infants control the movement of fluids and salts in the digestive tract
  • Play a role in helping an infant deal with chronic stress


The hormone leptin is made by the body's fat tissue. It controls appetite, weight, and how much energy the body uses. The leptin in breast milk may help to control a baby's weight. Studies show that when breast milk contains more leptin, babies have lower body weight. So, leptin may help to prevent obesity in breastfed babies.

Other Hormones Found in Breast Milk

Other hormones identified in human breast milk include gonadotropin-releasing hormone (GnRH), insulin, progesterone, estrogen, androgens, gastrin, adiponectin, resistin, and ghrelin.These hormones may also influence the baby's growth and development, but scientists are still exploring how.

A Word From Verywell

Breast milk contains a variety of hormones that impact a baby's growth, development, immune function, and other bodily systems. While the exact function of many of these hormones is still being investigated, these hormones are believed to be an important part of the nutritive value of breast milk and the health benefits it provides.

(Video) Overview of the Hormones in Breast Milk Bangla.


What hormones are in breast milk? ›

There are two hormones that directly affect breastfeeding: prolactin and oxytocin. A number of other hormones, such as oestrogen, are involved indirectly in lactation (2). When a baby suckles at the breast, sensory impulses pass from the nipple to the brain.

Which hormone causes let down of breast milk? ›

The let-down reflex is what makes breastmilk flow. When your baby sucks at the breast, tiny nerves are stimulated. This causes two hormones – prolactin and oxytocin – to be released into your bloodstream. Prolactin helps make the milk, while oxytocin causes the breast to push out the milk.

How are hormones important in the process of lactation? ›

In addition to prolactin, successful lactation also requires the hormone oxytocin. The hormone promotes milk ejection and the emptying of the breast. Oxytocin also is released from the pituitary gland into the blood, although from a different area (i.e., the posterior pituitary gland).

Can the hormones in breastmilk affect baby? ›

But other bioactive constituents in mother's milk, namely hormones, may also influence HOW the infant behaves. A growing body of evidence has demonstrated that hormones from the mother, ingested through milk, bind to receptors within the young.

What affects breast milk? ›

Various factors can cause a low milk supply during breast-feeding, such as waiting too long to start breast-feeding, not breast-feeding often enough, supplementing breastfeeding, an ineffective latch and use of certain medications. Sometimes previous breast surgery affects milk production.

What are the stages of breast milk? ›

Breast milk has three different and distinct stages: colostrum, transitional milk, and mature milk.

What is the hormone of breast development? ›

The hormone estrogen is produced by the ovaries in the first half of the menstrual cycle. It stimulates the growth of milk ducts in the breasts.

Do hormones in milk affect humans? ›

Sex Hormones Found in Milk

Recombinant bovine growth hormone (rBGH), which is a synthetic cow hormone that encourages milk production, has no detectable effect on humans.

Do stress hormones get in breast milk? ›

The cortisol in a mother's body can also end up in her milk. Babies appear to be remarkably sensitive to the hormone as they nurse. Scientists have found that drinking milk causes infants to rapidly build receptors in their intestines for detecting cortisol. The same shift doesn't happen when babies drink formula.

Are stress hormones released in breastmilk? ›

After birth and during lactation, mothers can still transfer physiological signals to the infant through the biological constituents of breast milk (Hinde et al., 2014), including cortisol. Cortisol concentrations are transferred from plasma to breast milk, as there is no mammary synthesis of cortisol (Hamosh, 2001).

What are 5 factors that affect milk production? ›

Genetic background, climate, diseases, feeding, year and season of calving have been reported to affect milk production, lactation length and dry period [2, 3]. Breed, age, stage of lactation, parity and milking frequency also influence performance production [2, 3].

What produces healthy breast milk? ›

Focus on making healthy choices to help fuel your milk production. Opt for protein-rich foods, such as lean meat, eggs, dairy, beans, lentils and seafood low in mercury. Choose a variety of whole grains as well as fruits and vegetables.

What causes increase in breast milk? ›

Hyperlactation — breast milk oversupply — can have many causes, including: Breast-feeding mismanagement. Too much of the milk production-stimulating hormone prolactin in your blood (hyperprolactinemia) A congenital predisposition.

What are the two types of breast milk? ›

The milk-making cells in your breasts all produce the same kind of milk. Foremilk is the milk available when your baby starts feeding, hindmilk is the milk your baby gets at the end of a feed.

What is breast milk called at first? ›

Phase 1: Colostrum

This is the thick first milk your breasts make while you are pregnant and just after birth. Moms and doctors may refer to it as "liquid gold" for its deep yellow color and because it is so valuable for your baby.

What color is breast milk? ›

A color that's normal for one mother might not be normal for another — so you shouldn't necessarily go out and compare color notes with all your breastfeeding friends. But in most cases, breast milk is lighter in appearance, usually white, although it can have a slightly yellowish or bluish hue.

What are the 4 stages of breast development? ›

What breast changes happen at puberty?
Female Breast Developmental Stages
Stage 4The areola and nipple become raised and form a second mound above the rest of the breast.
Stage 5Mature adult breast. The breast becomes rounded and only the nipple is raised.
3 more rows

Do breasts produce any hormones? ›

Estrogen in the Breasts

Tissues in the breasts actually produce small amounts of estrogen (although it is mainly made in the ovariesXThe female reproductive organs in which ova or eggs and hormones are produced., the corpus luteum follicles during menstruation, and the placenta).

What gland is responsible for breast development? ›

Mammary glands develop next and consist of 15 to 24 lobes. Mammary glands are influenced by hormones activated in puberty. Shrinkage (involution) of the milk ducts is the final major change that happens in the breast tissue. The mammary glands slowly start to shrink.

Which hormone is the main cause of milk? ›

Prolactin is a hormone named originally after its function to promote milk production (lactation) in mammals in response to the suckling of young after birth. It has since been shown to have more than 300 functions in the body.

Can crying affect breast milk? ›

Studies have shown that breast milk from distressed mothers may contain higher levels of cortisol. As your stress level rises, the level of cortisol in your breast milk also increases.

Can a woman produce milk without being pregnant? ›

Hormones signal the mammary glands in your body to start producing milk to feed the baby. But it's also possible for women who have never been pregnant — and even men — to lactate. This is called galactorrhea, and it can happen for a variety of reasons.

Does sadness affect breast milk? ›

Feeling stressed or anxious

Stress is the No. 1 killer of breastmilk supply, especially in the first few weeks after delivery. Between lack of sleep and adjusting to the baby's schedule, rising levels of certain hormones such as cortisol can dramatically reduce your milk supply.

What hormone is released when pumping? ›

Oxytocin also is released when a woman's breasts are stimulated by suckling or pumping, causing milk to move from the ducts and out the tiny holes in the nipple (let-down reflex). In the first few days after delivery, oxytocin also causes uterine contractions that help shrink the uterus back to its prepregnancy size.

What hormone makes you pumped? ›

Your adrenal glands make the hormone adrenaline and send it into your bloodstream. Adrenaline, a hormone your adrenal glands produce, has a purpose. It helps you face dangerous situations by causing temporary changes in your body. Your heartbeats and breathing get faster as part of the “fight or flight” response.

How long do mothers hormones stay in baby? ›

Under the influence of maternal hormones during pregnancy a newborn may exhibit signs of hormone exposure after birth, such as enlarged breasts. In a... This too is common and should be of no concern, disappearing within 2 weeks.

Does breast milk have estrogen in it? ›

When mothers take estrogen supplements, there is a very small amount of estrogen that ends up in human breast milk. The American Academy of Pediatrics has verified this is safe. There are naturally occurring hormones in all foods, including breast milk.

Does breast milk have human growth hormone? ›

“Interestingly, there are also several growth hormones in breast milk,” says St. Pierre. “Although I'm not sure that they actually benefit a human adult in any way.”

Does breastmilk have oxytocin? ›

Oxytocin is an essential lactation hormone released during breastfeeding that causes milk ejection and appears to have calming effect on the mother.

Does milk contain female hormones? ›

All milk (whether from cows, goats, humans, or porpoises) naturally contains small amounts of various hormones, including estrogen and progesterone. Because hormones like estrogen are fat-soluble, the level of hormones is higher in whole milk than in skim milk.

Is there progesterone in breast milk? ›

Summary of Use during Lactation

Because of the low reported levels of progesterone in breastmilk, even with the high-dose products, amounts ingested by the infant are small and would not be expected to cause any adverse effects in breastfed infants.

Which hormone is responsible for breast growth? ›

As a girl approaches her teen years, the first visible signs of breast development begin. When the ovaries start to produce and release (secrete) estrogen, fat in the connective tissue starts to collect. This causes the breasts to enlarge. The duct system also starts to grow.

Can babies have periods? ›

Baby girls can have some minor vaginal bleeding. It can start any time from 2-10 days of life. This is normal and called false menses. The cause is the sudden drop-off in the mother's estrogen (a hormone) after birth.

Why is it called witch's milk? ›

The term “witch's milk” comes from ancient folklore that fluid leaking from a newborn's nipple was a source of nourishment for witches' familiar spirits. 3 Galactorrhea is the result of the influence of the mother's hormones on the baby before birth. The mother's hormones can persist in the neonate's body for weeks.

What hormone causes release of milk? ›

Galactorrhea often results from having too much prolactin — the hormone responsible for milk production when you have a baby. Prolactin is produced by your pituitary gland, a small bean-shaped gland at the base of your brain that secretes and regulates several hormones.

Do emotions affect breast milk? ›

Feeling stressed or anxious

Stress is the No. 1 killer of breastmilk supply, especially in the first few weeks after delivery. Between lack of sleep and adjusting to the baby's schedule, rising levels of certain hormones such as cortisol can dramatically reduce your milk supply.

Are hormones used in milk production? ›

Bovine somatotropin (bST), also known as bovine growth hormone, is an animal drug approved by FDA to increase milk production in dairy cows. This drug is based on the somatotropin naturally produced in cattle.

What does human breast milk contain? ›

Breast milk is the best food for the newborn. Human milk consists of 87% water, 1% protein, 4% lipid, and 7% carbohydrate (including 1 to 2.4% oligosaccharides) (Figure 1). It also contains many minerals (Calcium, Phosphorus, Magnesium, Potassium, Sodium, etc…) and many vitamins.


1. Breastfeeding
2. Overview of the Endocrine System
(Dr Matt & Dr Mike)
3. Physiology of Breastfeeding (Letdown Reflex) and Breast Hormones – Made Easy
4. The science of milk - Jonathan J. O'Sullivan
5. Parturition - Pregnancy, Hormones, Giving Birth
(Armando Hasudungan)
6. Endocrine System | Summary
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