The Science of Breast Milk: What Makes It Liquid Gold?

Breast milk is a complex and highly nutritious food for infants, which is why it is sometimes referred to as “liquid gold”. Its composition cannot be replicated completely and it has unique benefits that other baby milk substitutes don’t. To show you how truly incredible breast milk is for babies, we’re going to explore the science behind breast milk’s composition, production, storage, and benefits for mum and baby.

The Science Behind Breast Milk Production

The Anatomy of the Breast and Milk Production

Understanding the structure of the breast is key to knowing how milk is produced and delivered to your baby. The breast is made up of specialized tissues, ducts, and glands that work together to create and transport breast milk efficiently.

• Mammary Glands and Milk Ducts

At the core of milk production are the mammary glands, which contain tiny alveoli—milk-producing sacs lined with specialized cells. These alveoli are grouped into lobules, which connect to an intricate system of milk ducts that carry milk toward the nipple. When a baby suckles, the milk ducts contract, allowing milk to flow.

• The Nipple and Areola’s Role in Breastfeeding

The nipple serves as the exit point for milk, with multiple small openings where ducts release milk during nursing. Surrounding the nipple, the areola contains Montgomery glands, which secrete natural oils that keep the skin hydrated and protect against bacteria. This helps support a secure and comfortable latch for the baby.

Anatomy of the Breast​

How Is Breast Milk Produced?

Two breastfeeding hormones are involved in breast milk production: prolactin and oxytocin. When your baby latches onto the nipple, sensory signals are sent to your brain, triggering the release of prolactin, which tells your body to make more milk. At the same time, oxytocin steps in to help, causing the milk ducts to contract and gently push the milk toward the nipple, this is known as the let-down reflex. This incredible cycle keeps your milk supply flowing and adapts to your baby’s needs with every feed.

During pregnancy, your prolactin levels increase, which promotes the growth and development of the mammary tissue in readiness to feed your newborn baby. However, other hormones present in pregnancy, such as oestrogen and progesterone, stop the breast milk from being released until after your baby is born.

As the levels of progesterone and oestrogen drop, prolactin kicks in to start breast milk production which is when you will start to see colostrum. The raised prolactin in the first few days postpartum results in your milk “coming in” and your milk turns from colostrum to more mature milk.

Your prolactin levels are at their highest roughly 30 minutes after a feed so that it can start to produce breast milk for your baby’s next feed.

Stages of Breast Milk

Colostrum: The First Milk

Colostrum is the first milk your body produces after your baby is born. Colostrum is thicker and has a tinge of yellow - which is where the term “liquid gold” comes into play! It lasts for up to 3 days until your milk starts to come in and it slowly turns white.

Colostrum is rich in nutrients, proteins, antibodies, and vitamins which gives your baby a fantastic start to fill their tiny tummies and build their immune system. Expecting mums can use colostrum syringes to harvest colostrum in the build-up to the birth and the first few days postpartum.

Colostrum harvesting means using a syringe or colostrum harvesting kit to collect colostrum from the breast and safely store it until you can feed it to your baby, regardless of whether you plan to breastfeed or not. It can be useful to have, especially if your baby requires extra care or is born prematurely.

Read more to learn how to collect colostrum and how to store colostrum.

Transitional & Mature Milk

You will notice your breast milk slowly change from day 3 postpartum as it transitions from colostrum to a thinner consistency. Over time your milk will mature (from 4 weeks) and you will develop foremilk and hindmilk.

Foremilk is expressed first and is the watery part of milk. Foremilk is high in lactose with a lower fat content and will be clearer in colour. Babies feed on breast milk not only to satisfy their hunger but also to stay hydrated, which is why the watery content of foremilk is important. The longer your baby suckles at the breast the hindmilk comes through which has a higher fat content making it creamier and more filling.

The Amazing Composition of Breast Milk

Breast milk is one of nature’s incredible creations. The composition of breast milk not only has immune-boosting properties but is rich in nutrients to support your baby’s growth and development.

Breast milk’s key components are protein, fat, prebiotics, probiotics, vitamins, and other bioactive factors. With breast milk being actively studied, it is clear that breast milk goes beyond delivering quality nutrition.

Prebiotics (oligosaccharides) encourage the growth of healthy bacteria in the gut meaning it is harder for pathogens to pass through the wall of your baby’s gut and make them ill. Antibodies transfer from the mother to her baby meaning that their immune system grows stronger.

The only recommended vitamins for breastfeeding mothers to supplement with breast milk are B12 and Vitamin D. Depending on the mother’s diet, they could be deficient in vitamin B12. Vitamin D is not present in breast milk so your baby will require this supplement to support the development of healthy bones.

As your baby grows, breast milk rapidly changes to adjust to your baby’s needs. It adapts to their health, growth, and development from the moment your baby latches.

The Hormonal Science Behind Breast Milk Production

Breast milk doesn’t just exist within us until it’s called to action. There are hormonal changes within the body that start during pregnancy and begin to stimulate the production of breast milk.

Now we know what part the hormones prolactin and oxytocin play in breast milk production, it helps us to understand the hormonal shift from pregnancy to postpartum. It also explains how you can maintain your breast milk supply and why you experience the let-down reflex.

The Let-Down Reflex

Let-down can be triggered by your baby when they start to nurse at the breast. You might feel a tingly feeling in the breast as your breast milk begins to flow. Initially, your let-down can flow quickly and gently ease off while your baby continues to breastfeed. Other things besides your baby nursing can trigger the let-down reflex such as:

• Hearing a baby cry

• Seeing photos of your baby

• Feeling strong emotions, thinking of or seeing your baby

• Using a breast pump to express

• Massaging the breast to bring on breast milk

Dysphoric Milk Ejection Reflex (D-MER)

Dysphoric Milk Ejection Reflex is a medical condition that affects a small number of breastfeeding mums. It is a physical reaction that happens before the let-down reflex starts. It causes nursing mothers to feel sadness, anxiety, and other negative emotions for a few minutes and goes away as the feed continues.

There is nothing that breastfeeding mothers have done to cause this dysphoria and it is not to be confused with postpartum depression. There are resources and support tools you can access to learn more, shared by Alia Macrina Heise, IBCLC Retired.

What Affects Milk Supply?

Oxytocin is the hormone that allows the breast milk to flow. When the production of oxytocin is hindered, you will notice a change in your let-down reflex and your breast milk supply. Stress is a common factor that lessens your oxytocin levels and contributes to the decrease in breast milk supply.

As your baby grows, their feeding patterns will change and over time your baby will drop a feed. Each time this happens your breast milk supply will adjust so you do not feel engorged. On the other hand, frequent nursing on both breasts will increase your supply of breast milk because each time the breast is emptied, your body will start to produce more breast milk for the next feed.

Other factors that can affect your breast milk supply are:

• Diet - eating foods that decrease or increase your breast milk supply

• Nipple soreness - irritated skin or cracks due to dryness can be painful leading to shorter or fewer feeds as it heals

• Poor latch - your baby needs to latch correctly or breast milk will not be extracted efficiently, leading to a decrease in the milk supply

• Expressing using a breast pump - a great tool to use to increase your breast milk supply if it starts to drop

Proper Storage and Handling of Breast Milk

Ensuring the safe storage and handling of breast milk is essential to preserve its nutritional and immunological benefits for your baby. Adhering to recommended guidelines helps maintain milk quality and reduces the risk of contamination.

Storage Guidelines

• Room Temperature (77°F or 25°C or colder): Freshly expressed breast milk can be kept at room temperature for up to 4 hours. 

• Refrigerator (40°F or 4°C): Store milk in the back of the refrigerator, where temperatures are most consistent. Freshly expressed breast milk can be refrigerated for up to 4 days; however, using or freezing it within 3 days is optimal. 

• Freezer (0°F or -18°C or colder): For best quality, use frozen breast milk within 6 months, though it is acceptable to store it for up to 12 months.

Choosing the Right Storage Containers

Selecting appropriate storage containers is crucial for maintaining breast milk's safety and quality. Use clean, food-grade containers made of glass or BPA-free plastic with tight-fitting lids. Avoid using disposable bottle liners or plastic bags not intended for breast milk storage, as they may not be durable or safe. 

For a convenient and reliable storage solution, consider Lola&Lykke Breast Milk Storage Bags. These pre-sterilized, BPA-free bags are designed to simplify the milk storage process. They are compatible with the Lola&Lykke Smart Electric Breast Pump, allowing you to pump directly into the storage bags, reducing the need for transfers and minimizing potential contamination.

The bag also transforms from a mother milk storage bag to a baby bottle simply by attaching a bottle teat to the adapter. The bags can stand upright for easy filling and lay flat for efficient freezing and thawing, preserving essential nutrients and vitamins in your breast milk.

Learn more tips and tricks on mother milk storage.

Attaching your pump to a milk storage bag can simplify your pumping and feeding routine!

Freezing and Thawing Breast Milk

When freezing breast milk, label each container with the date it was expressed to track storage times accurately. Freeze milk in small portions (2 to 4 ounces) to minimize waste and allow for quick thawing. Place the containers in the back of the freezer, where temperatures are most stable.

To thaw frozen breast milk, place it in the refrigerator overnight or hold the container under warm running water. Avoid using a microwave to thaw or heat breast milk, as it can create hot spots and degrade valuable nutrients. Once thawed, breast milk can be refrigerated for up to 24 hours but should not be refrozen.

Breast Milk Beyond Feeding: Unexpected Uses

Due to the incredible nutritional qualities breast milk has, nursing mothers over the years have used breast milk for other purposes to support the health and development of their babies.

Baby Care Uses

Expressed breast milk can be used to help with cradle cap where your baby’s hair grows, for example on the top of their head or in their eyebrows. It’s a natural remedy that can remove thick cradle cap from areas where it has built up.

Breast milk can also be used for your baby’s skincare routine. It’s common for babies up to 2 months old to have “baby acne” on their skin. The cause is unknown but it is believed that the hormones in the placenta can change how your baby’s skin produces sebum. Sebum protects the skin and hair but too much sebum can clog the pores and lead to baby acne.

You can add expressed breast milk into your baby’s bath to create a milk bath, gently wash their skin with it, or massage it directly onto their acne. Breast milk has anti-bacterial and anti-inflammatory properties which may help reduce baby acne, however, there is no scientific evidence to prove this.

Health Benefits for Mums

Studies have been conducted over the years to prove whether exclusive breastfeeding that continues for a prolonged time affects the probability of developing a pelvic floor disorder or overflow incontinence. With the few studies that have been researched, it was proven there was no link between exclusive breastfeeding and these conditions meaning breastfeeding could have more health benefits for nursing mothers than anticipated.

Breastmilk Jewellery

Your breast milk can be made into a precious keepsake to celebrate your breastfeeding journey. Some designs also celebrate how long you have breastfed and incorporate personalised engravings. You express a few drops of breastmilk and send it to a jeweller who can set your breast milk into jewellery.

Conclusion

I think you can agree, breast milk is pretty incredible. Whether your baby has a few drops or continues to breastfeed into their toddler years, every drop counts towards their health and development.

Expectant and new mothers can seek support to gain an understanding of proper breastfeeding techniques, how to store breast milk and address common challenges. Every breastfeeding journey is different and we are here to support you every step of the way.