In this section, we’ll introduce what you need to know for pumping effectively and comfortably. We won’t go too deeply into breastfeeding itself, as there are excellent resources out there which do a better job. Click here for a list of those.

Your anatomy

🍒 To learn how to pump well, you need to learn more about what your breasts are going through. Hint: a lot.

First, we’re going to break down your anatomy in detail, how your breasts make milk, and what happens to your breast (and in fact your whole body) when a baby feeds or you pump.


Your breast

Let’s start with the anatomy of a breast.

[insert diagram - surface]

On the surface, the visible part of the breast is the same for most people: the areola and the nipple. But for the female[1] breast, the anatomy is different, all created through marvellous evolution so that we can produce milk and breastfeed.

So here’s what a breast looks like inside.

[insert diagram - inside]

Your breast has three types of tissues:

  1. Glandular tissue — Responsible for producing the milk
  2. Fatty tissue — Determines the size of each breast
  3. Connective tissue — A fibrotic tissue responsible for holding the glandular and fatty tissue in place

Glandular tissue is involved in milk production and is made up of many glands called lobules.

The lobules look like a bunch of grapes and each lobule gland has tiny sacs called alveoli that produce and hold milk. Similar to the stem that holds grapes together, lobules are connected by terminal ducts that help transport the milk from the lobule out to the nipple through the milk ducts. Read more on exactly how milk gets made and pushed through your breast here.

Your areola and nipple

Areolas are typically round and darker than the rest of the breast. Areolae have their own set of glands called Montgomery glands, which secrete oil to help lubricate the nipple and skin to prevent chafing while breastfeeding.

Why are they called Montgomery glands? After an Irish obstetrician who studied changes in the nipple over pregnancy, in the early 1800s. He got some things right, and some things less so - read more about these here.

The nipple refers to the smaller section near the middle of the areola that typically sticks out when stimulated. There are approximately nine milk ducts in each nipple that are used to get the milk out of the breasts. Read more on how you make milk here.

Nipples and areolae can vary in shape and size and that variation is normal. We know from our own surveys at Milkdrop that nipples alone can range from 5 mm to 40 mm. They can also be long, round, flat or inverted, and anything in between. On top of this, your two nipples may be different from one another. They’re sisters, not twins!

[insert bank of nipples - different sizes & shapes]

Why we don’t know that much about the size and shape of lactating nipples

While there is a huge body of research on the anatomy of the nipple, it’s not quite in the way you might think.

We know surprisingly (and embarrassingly) little about the size and shape of the female nipple. This means it’s hard to design products like breast pumps for them.

Most of the nipple-y research seems to focus on two areas.

Plastic and reconstructive surgery

Much of this research is about how to create the “ideal” nipple for attractiveness. Surgeons need guidance on how and where to create and place the nipple for augmentation or reconstructive surgery, but still. Ugh.

Surely the most “attractive” nipple is the one you have?

Not so. There are other characteristics typically determined by asking study participants to rank ‘attractiveness’ based on models or photographs of people’s breasts. These include breast width to upper buttock width ratio, nipple direction, breast width to shoulder width ratio and breast projection (i.e. sagginess).

Some papers do talk about the patient’s own feeling of attractiveness, rather than someone else’s view of her attractiveness. It still feels odd to have created an environment where a woman feels her attractiveness is dependent on her nipple placement and shape, and then funded more research into defining that attractiveness better.

Identifying nipples in images

Another investment area in understanding nipple shape is for developing algorithms that accurately and efficiently identify nipples within images. Ostensibly to identify pornography (fair enough), these algorithms are also behind defining ‘sensitive’ content on social media platforms, which often can simply be a …. lactating nipple. This area of research isn’t quite as frustrating as the first one, because the algorithms are also used in the software behind mammograms and other health technology.

To show you the scale of this issue, we have counted x studies specifically on the size, shape and function of the lactating nipple.

We are not intending to be rude to researchers, surgeons or people who are beneficially affected by the research and development we describe above. We would just like to see an equal (if not more) level of effort and funding to understanding the lactating nipple and supporting people to feed breast milk to their babies.

How your breast changes

You may have noticed your breasts change during pregnancy. Not only do breasts typically get bigger, but the areolae and nipples also undergo changes during pregnancy. The visible changes to the areola and nipple are caused by hormones and promote breastfeeding.

The areola and nipples get visibly darker and larger during pregnancy for most people, which we think helps the baby see the contrast in color between the areola and the rest of the breast. The Montgomery glands on the areola may also be more noticeable during pregnancy, although not always. In later pregnancy, you may even notice a sticky secretion from these glands, or perhaps you might see that water beads more when it’s on your breast. This is the secretion from the Montgomery glands as your breast prepares for lactation.

Here’s a list of the things that change during each trimester:

  • First trimester: Your system of milk ducts grows and branches out into your fatty tissue (thanks to more estrogen running through your body)
  • Second trimester: Your mammary glads are ready to produce milk
  • Third trimester:

  • Nipple colours – pale, dark, red
  • How nipples change through pregnancy, breastfeeding or pumping
  • Which nipples are “best” for breastfeeding
  • Which nipples are “best for pumping
  • elastic nipples
  • breast anatomy – nipple
  • breast anatomy – nipples


How you make milk 


You make milk when messages from your breast travel to your brain, which trigger hormones, which then travel through your body, to tell your breast to make milk.


Your breast systems

You need three kinds of systems to make milk:

  • alveolar cells
  • myopithelial cells
  • blood supply (via capillaries)

The alveolar cells create and contain the milk, they’re hollow and the milk is made in them.

The milk gets pushed out along the ducts to the nipple by the myopithelial cells (kind of like the uterus lining that contracts when oxytocin hits it).

The blood supply is there to bring hormones and nutrients to the receptors, which are on the outside edge of your alveolar cells.

We didn’t always know the anatomy so well. There was some comprehensive study of lactating breasts in the 1840s, but it wasn’t until 165 years later that researchers ultrasounded lactating breasts, and showed that we had misunderstood quite a few things about how your breast and baby works to feed. Read this study, and this study for their learnings from ultrasounds.


Fun fact: this ultrasound research was funded by Medela (you know, the yellow breast pump brand) - it’s nice to see a long-term contribution to research like this from pump manufacturers.


🤔 Why are we focusing so much on this when we should be talking about pumping? Because understanding what is going on in your breast is important for understanding how to best set yourself up for pumping.


4 common misconceptions you may have about your breast that could affect your success pumping

  • Your ducts aren’t evenly spaced like a clock around the breast.

You may have more ducts around some parts of your breast than another. This is why when you pump, you may get better flow in one part than another part. Also, it may explain why you may seem to experience blocked ducts in some parts of your breast, but not others.

  • You have about 3 to 5 functional pores in your nipple where your milk comes out.

This is a bit different to a common idea out there that you have 25 to 30 squirting nipple pores in your nipple.

  • Your fat isn’t sitting behind your breast, or in one particular spot.

It’s actually all mixed up with the glandular tissue in your breast. Some of that fat even comes out in your milk.

  • Although you may feel like one, your nipple and breast is different from a cow or a goat.

Those animals have lactiferous sinuses, which are storage cavities in the teat that hold milk. Humans don’t have this. Your milk goes straight from your lumen (the little grape-like looking sac that creates and holds your milk) to the nipple.


Where do these misconceptions come from?

You can be forgiven for not knowing this. A few of these misconceptions come from the early 1800s (about the time of Netflix’s Bridgerton series if your history isn’t your strong suit), when breast anatomy was being studied through dissection by two men - Sir Astley Paston Cooper, 1st Baronet and William Fetherston Haugh Montgomery.

Apart from both having very long, rather fancy names, and both having a propensity for naming parts of the female breast after themselves (Montgomery Glands and Cooper’s Ligaments) (which feels a little creepy in the modern day), they both made advances and errors in what we know and assume about the breast.

To be fair, they didn’t have ultrasounds to confirm their studies (that came 165 years later - they were injecting hot wax into milk ducts to try to define their shape.

Why it took over a century and a half (from 1840 to 2005) to really study the anatomy of the lactating breast, when we know breast milk to be critical in developing babies, we don’t know.

👆Here is a drawing from one of Montgomery’s books, looking at nipple changes during pregnancy.



Prolactin and oxytocin are the two main hormones that directly impact milk production.

Both already exist in your body, and both are secreted from the pituitary gland, deep inside your brain. They each have different pathways, which means they are triggered in different ways.



Let’s start with prolactin, which is the one that makes the milk.

As we mentioned before, prolactin already exists in your body. After birth, you’ll see a big increase, with some people increasing faster and higher than others.

You don’t need to be a breastfeeding mother to make it. Here’s a case of a woman, who had already been through menopause, who established breastfeeding.

Prolactin and your nervous system

To understand how prolactin works, you need to understand a little bit about your nervous system. One of the functions of your nervous system is to take information that you sense around your body, process it, and trigger reactions.

Too vague? Fair enough. Let’s imagine that you touch a hot stovetop. The heat creates pain signals that travel back to your central nervous system (your spinal cord and brain) that cause you to pull your hand away.

In the case of feeding, your baby sucks at your nipple, which sends a message through the nerve (called T4) that runs from your nipple to your spinal cord up to your brain. Your brain secretes prolactin to your blood, which runs all the way back through your body and to your breast to create milk (pro - lactin = pro - milk!).

Stimulating your nipple (and your breast) to increase prolactin

Now, it doesn’t have to be a baby that sucks at your nipple for this message to be sent and responded to. Theoretically, it could be a pump or your hands. It’s just that a baby is very good at stimulating the nipple by latching, and also at stimulating your breast with their body.

There are two other nerves (called T3 and T5) that run from your breast above and below the nipple that also send the signal to release prolactin when stimulated. Have you ever seen a breastfeeding baby massage or play with their mother’s breast?

[insert gif of baby playing with breast]

So if you’re trying to increase your prolactin, you would spend time early on stimulating your nipple (T4) AND your breast (T3, T5), although the nipple is most important. Check out this study, that shows the highest level of prolactin release occurs when you stimulate nipple and breast, as opposed to just breast.

Timing of stimulation to increase prolactin

Now as with all things in the human body, it’s never that simple. Your prolactin response and levels aren’t the same every time you stimulate your nipple. One study showed prolactin levels rising at about 25 - 30 minutes into a feed, and dropping off between feedings. The longer the period your baby is away from your breast, the less prolactin you have.

This is supported by other studies that show that more frequent nursing (10x per day) resulted in more weight gain for babies at Day 15, than less frequent nursing (7x per day), even though the total time nursing was the same (137-138 minutes).

Unfortunately,again, we couldn’t find any studies looking at the effect on prolactin from pumping (as opposed to nursing).

Creating receptor sites for prolactin

In the first few hours after your placenta is no longer in your body, your hormones have a big change.

Happens early - first two hours after birth - get more receptors



Prolactin increases during pregnancy, which helps increase the mammary glands to prepare for milk production. Suckling at the nipple stimulates milk production by increasing prolactin blood levels.

There is a balance of prolactin and oxytocin necessary for producing the milk and keeping it in the breast. Oxytocin makes the cells in the breast tissue (alveoli) contract, which allows the milk to be collected in lobules. When oxycontin is produced more quickly than prolactin, the milk is released from the alveoli and travels through the ducts. Skin-to-skin contact also promotes oxytocin release. Both prolactin and oxytocin levels are stimulated by suckling at the nipples.

How feeding works

We’re talking all about pumps and pumping in this guide. To do that well, we need to understand what a pump is there to do, which is remove milk from your breast by mimicking a baby (as best it can).    

What does a baby do to feed at the  ?

A healthy baby uses their jaw to suck and compress to remove milk from the breast. But it’s not quite how you might first imagine it.

Here’s what is happening when a baby once latched, is suckling well.

Image of baby opening jaw






Image of baby drawing nipple back

Image of baby compressing nipple

Lowering the jaw to create suction

Pulling the nipple back and pulling milk out of the nipple

Compressing to slow flow to swallow and breathe

A baby creates suction (a.k.a vacuum or negative pressure for physics nerds out there) by lowering her jaw. That suction helps to pull back the nipple, which draws milk out of the nipple into the baby’s mouth. She then compresses the breast with her jaw, and the ducts of the mammary gland within it, which stops (or slows) the milk coming out of the nipple and allows her the swallow the milk in her mouth and open her airway to breathe.

So it’s not her closing her jaw that draws out your milk, it’s opening it.

It seems counter-intuitive but think about a baster from the kitchen. You put the long tube into the sauce, then you squeeze (compress) the bulb at the top. The liquid doesn’t actually run up the tube until you release the bulb. That’s because you’re creating suction by opening up the bulb.

By opening her jaw, your baby is ‘releasing the bulb’ and creating suction to draw out your nipple and milk.

How do we know all of this?

The science of milk ‘removal’ or ‘extraction’ has been studied for some time. Scientists and clinicians have looked at the biomechanics of sucking and breathing patterns of babies feeding at the breast and the bottle. Some studies have observed babies feedin and others have even used ultrasound to try to see what’s going on inside the breast and baby’s mouth[4]. Until the ultrasound studies, there was some disagreement about how infants actually transfer milk from the breast[5], but that seems to have settled now. The next focus for research looks to be  

Ultrasonography of breastfeeding pairs demonstrates that milk transfer occurs in response to the intraoral vacuum generated by reflex downward excursion of the jaw, at the same time as the mammary ducts contract with milk ejection. The infant tongue moves downward as a single unit in tandem with jaw depression (Douglas & Geddes, 2017; Geddes & Sakalidis, 2016).[6]


Your breast pump

Breast pump anatomy

  • breast pumps - what are they
  • pump – general
  • pump general
  • History and development of pumps

How breast pumps work

A breast pump works by repeatedly sucking your nipple against a plastic funnel until milk flows from your nipple.

  • How does a pump work - diagram + parts (refer to section 2) 
  • How breast pump works

Pump vs Baby

Why do pumps feel different from your baby?

In theory, a pump sucks at your breast to pull milk from your nipple. They are typically designed to mimic your baby’s suck as closely as possible, in terms of the strength of the suck itself, and also the rate and rhythm they suck with. 

But like any machine, they are rarely quite as good as the real thing. Although pumps can be a very effective tool for expressing your milk, they are a bit of a blunt instrument compared with a baby.


  1. Pumps mostly just suck. Pumps typically only use suction as the main method for extracting your milk, whereas a healthy infant will use a combination of sucking and compressing with their jaw. See here for more detail on that.  Pumps also don’t do any of the other things your baby might. For example, pumps don’t compress your nipple when sucking, they don’t grab at your breast like some babies do (which can help to stimulate letdown). They certainly don’t give you that gooey, emotional feeling that your baby can give you, which can help some women with letdown.
  2. Pumps are often made from quite harsh materials. The flange is typically hard plastic or hard-ish silicone. While these flanges are made to fit as many women as possible, the hard surface and often sharp angles at the flange, doesn’t support your nipple all the way around as it moves, in the way that a baby’s mouth and tongue might. 
  3.  Pumps aren’t as smart as your baby. A healthy infant not only has a more complex way to get milk from your breast than a pump, they also adapt and learn how to best remove your milk by changing their sucking pattern, rate and strength. And, remarkably, your breast responds to this by matching supply.

With Artificial Intelligence and machine learning, it’s possible that pumps could ‘learn’ your body. Perhaps that’s something to look forward to when you have your next baby.



New vocabulary

There’s a whole new vocabulary, and a load of abbreviations, to learn when it comes to pumps.

Both medical and cultural ones.  For example, what do we mean exactly by milk expression versus milk transfer, how is exclusive expressing different from mixed-feeding, what is EBM,  

Visit our glossary for a complete list of words you never knew you needed to know.

What is breastfeeding?

There are so many definitions for the term “breastfeeding”.

Some people (and studies) say that breastfeeding should include only babies who are exclusively breastfed – they are only receiving breast milk in their diet, and nothing else. It’s often not clear if breast milk from pumping is included as part of this group (which we think they should, given the baby is receiving breast milk!). Those studies also don’t count babies who are receiving formula top-ups or who are ‘mixed’-fed or ‘partially breastfeeding’ as being breastfed. These babies are still receiving breast milk (and the benefits of it) as part of their diet.

More recent studies have started to break breastfeeding into two categories: exclusive breastfeeding and non-exclusive (or partial) breastfeeding.

Culturally, there’s a lack of awareness about pumping as a way to provide breast milk to your baby. If you pump, chances are high (anecdotally) that you’ll be asked “why aren’t you breastfeeding?”. This can be frustrating and deflating, because it can feel like you’re doing everything you can (you’re attached to a mechanical pump after all!) to feed breast milk to your baby, so they are breastfed. Many women who come to pumping do because they and their baby are having difficulty latching, or because they’re in pain, or their milk supply doesn’t seem to be growing 

On top of cultural

Am I breastfeeding if I am breast-pumping?

[comment about breastfeeding and pumping – language vs clinical conflict ]

Am I breastfeeding if I am breast-pumping and doing top-ups with formula?

[comment about ‘minimum’ amount of breast milk required to derive benefits?]