Anatomy of the Breast & Mechanics of Infant Suckling

“Nursing” by Alex Grey



And Then There Were Two

Breasts are so important, they develop long before they will be needed for their purpose. In fact, breasts make their very first appearance during the sixth week of embryonic development when milk lines (mammary ridges) are formed.

The process is begun in males too, even though they will never need to nourish a child with them. Sometimes babies of either gender even produce a bit of ‘witch’s milk’ a few days after birth as a result of mom’s lingering lactation hormones that passed to the baby in utero.

Male breasts have all the same components as female breasts, however the ducts remain undeveloped. Male breasts can look more like female breasts if they gain fatty tissue, though many females have virtually no fatty tissue on their chests and that’s normal, too (our culture is just not used to seeing female breasts that look this way). Male ‘pecs’ are the result of building up the pectoral muscles, which females can do as well.

Basic biology lessons from Ken L. Smith at

“Tanner Stages” is used by the medical community to describe the change in external appearance of breasts over time, but it fails to explain the important changes happening inside them. It also neglects to discuss male breast swelling during puberty, which is temporary but very common.

“One for here, one for the road! Via

Breast Varieties

Wanna feel special? Well, humans are the only mammal of which the female’s breasts remain enlarged after puberty, not just during pregnancy. How mysterious and intriguing!

One theory is that when our predecessors began walking upright, the breasts evolved to become a ‘frontal counterpart’ to the buttocks. Other ideas include: breasts are also meant to act as cushions for infants’ heads while bedsharing; are a form of competition between females to prove maidenhood; and possibly, that noticeably present breast tissue is really just ‘an evolutionary flaw’ (hey, nature…it happens).

“The shape of the human breast may reflect a compromise between sexual signaling and feeding functionality. Human breasts are much larger than in other primates, possibly because they serve as costly signals of fecundity and access to sufficient food resources…So it may be that sexual selection puts pressure on females to develop more obvious and costly signals of their fertility and quality at the cost of complicating nursing.” – Anthony A. Volk, Journal of Social, Evolutionary, and Cultural Psychology

There is a wide variety of breast appearances, and all are actually ‘normal.’ While generally all are normal looking, a breast is considered normal in function if it has enough milk ducts to make milk for a potential baby, regardless if they end up being put to work in the milk factory.

There is no ‘breed’ most suitable for breastfeeding: flat, heavy, pointy, long, tall, grande, venti… they can all get the job done just as effectively! Even great variations in storage capacity between women is totally normal, and it doesn’t affect breastfeeding in any way other than how often a baby will need to nurse (read more on milk storage capacity here).

However, there are a few less usual breast anomalies, some of which may limit milk production.

Atypical conditions:

  • Asymmetry – Is one always looking you in the eye and the other keeping a sidelong gaze? Does one seem to sit up high on a throne while the other is kinda hanging on for dear life? You might have even given them nicknames, like ‘Blossom’ and ‘Rosebud,’ or ‘Big Boss Lady’ and ‘Underling.’ Nevertheless, they make a popular pair: asymmetry in size or position is very common, and typically it doesn’t cause breastfeeding problems. About 75% of women find that they make more milk in one breast (the ‘super-producer’) than the other, and this itself is no cause for concern either.
  • Gigantomastia – Also related to macromastia. Read more about it here.
  • Hypoplasia (IGT) – Also known as Insufficient Glandular Tissue. Women with this condition marked by underdeveloped milk ducts often experience challenges with making enough milk. Read more about this condition here.
  • Supernumerary/Polymastia – Ancient fertility goddesses are famously depicted with rows of supernumerary breasts, and extra breasts and nipples were considered Devil’s Marks during the era of witch hunts. But an extra breast, also called an accessory breast, is not just an anomaly of legend or pop culture.

A breast in addition to the original pair is surprisingly not uncommon today as it affects between 1-2% of the population (and possibly as high as 6% due to high incidence of misdiagnosis). Ectopic breast tissue may not become evident until either pubertal hormones are released or during pregnancy.

The Southern Medical Journal (Department of Pathology and Laboratory Medicine, Emory University School of Medicine) describes polymastia:

“[A polymastic breast is] a normally shaped female breast with a nipple and areola. In attenuated forms it may be breast tissue with nipple lacking areola, glandular tissue with areola but without nipple, or only ectopic breast tissue with neither areola nor nipple.

The genesis of extra breasts lies in hidden, quiescent primordial breast tissue along ‘Hughes lines,’ also known as mammary lines or simply ‘milk lines.'”

According to this in-depth historical overview of polymastia, Charles Darwin theorized that this condition is one of atavism (an “evolutionary holdover”):

“[Polymastia is] an evolutionary throwback. The embryo at one point resembles a fish, then a reptile, and so on until it becomes a recognizable human form. More primitive mammals beneath humans on the evolutionary scale have multiple breasts arranged along milk lines. When such a primitive reversion manifested itself in women, Darwin saw a proof of evolution in this atavistic fingerprint. In this view, multiple breasts and nipples are considered obsolete parts, such as wisdom teeth and the appendix.”

How does polymastia affect breastfeeding? There are many reports of women nursing from supernumerary breasts (including the 1827 case of Therese Ventre of Marseilles who nursed her five children from three breasts!), though the extra tissue can become tender during menstruation, pregnancy and lactation.

Blogger Scary Mommy ended up discovering a third mammary gland in her armpit that actually lactated. Supernumerary breasts may not always include milk glands, however.


Did you know that experts say female breasts haven’t actually reached full maturity (even after puberty) until a pregnancy; that this time in which the breasts lay down lactation receptors is actually the true final stage of development?

During pregnancy, fatty tissue is lost and replaced by growing internal milk-making structures, hence why many breasts increase in cup size yet others don’t appear to change much. It depends on the ratio of fat to ductile and connective tissue prior to pregnancy. Losing or gaining weight changes only the amount of surrounding fatty tissue and has no effect on the amount of ductile tissue.

If a woman doesn’t breastfeed for some time after birth, then the milk-making factory that her body has built gets bulldozed, if you will. This atrophying of the lactation system is called involution (it also occurs after weaning and during menopause).

Here we have the Anatomy of a Working Breast (includes history, development, stages, physiology, and describes how substances enter milk). Shockingly little investigation has been conducted on lactating breast anatomy for the past 150 years; past understanding about breast structures were recently found to be incorrect.


The lactation system inside your breasts resemble a tree. The milk glands (the leaves) are grapelike clusters of cells high up in the breast that make milk. Milk travels from these glands down through the milk ducts (the branches). These ducts then widen beneath the areola (the dark area surrounding the nipple), forming milk sinuses (the tree trunk), which then empties into the approximately twenty openings in your nipple (like the channels going down to the roots of the tree).” – Dr. Sears


“Sagging.” Sounds depressing, right? As if a sagging breast is weighed down by sadness into the shape of a frown, or something to such melancholic effect.

Let’s be real and call them what they are: real, and beautiful!

Sagging breasts have proved their power — from either having a grand ol’ journey living a lotta life, or spending time on a woman who was busy making and sustaining life. Sagging breasts and nursing breasts have the best stories to tell, you see.

“Nursing does not diminish the beauty of a woman’s breasts; it enhances their charm by making them look lived in and happy.” – Robert A. Heinlein

MaiTai gives his mama some breast support!

MaiTai gives his mama some breast support!

So I’m sure you’re wondering, what actually contributes to the ‘dreaded’ downward drag?

  • Age (guess what, everyone ages)
  • Pregnancy
  • Smoking status
  • Weight loss & eating habits

“[P]rofessor Jean-Denis Rouillon from Besancon, France, has published a study (2013) that shows that wearing bras may increase sagging. The 15-year study involved 330 volunteers between the ages 18 and 35. Researchers measured their breasts using a slide ruler and a caliper and recorded any changes throughout the study period. Women who did not wear bras had a 7 millimeter lift as measured from their nipples each year. Their breasts were also firmer, and their stretch marks faded. There was also no evidence that the bras helped get rid of back pain.

The idea is that when you wear bras, the muscle tissue that supports the breasts may not develop as well. Also, the Cooper’s ligaments inside breasts can atrophy and shrivel away from not being used. ‘Use it, or lose it’ seems to be at work!” – 007 Breasts

Breastfeeding, you’ll notice, did not make the list of droop-factors.

One mother was quoted in The Breastfeeding Book: “In the end, gravity gets us all.”


“With weaning, the milk glands atrophy or shrink to almost nothing [‘involution’], and obviously the breasts decrease in size correspondingly. However, after the milk glands shrivel up, the body starts depositing some fat back to the breasts. Remember, [a] lot of the fat left the breasts during pregnancy…

After weaning, over a period of up to 6 months, the body deposits fat back to the breasts. With gradual weaning, often there isn’t any abrupt change in breast size, but the fat-depositing process can take place at the same time with the slow weaning.

If the weaning is abrupt, the breasts will dramatically decrease in size and can look like ’empty balloons.’ If the weaning is gradual, this will not happen. At any case, eventually fat fills breasts again and the breasts will regain their pre-pregnancy size or close to it.” – 007 Breasts

Nipple Varieties

Though there are marked variances between individual females, the over-saturation of unrealistic breast representations in our society and the censorship of normal female anatomy in the media have together resulted in skewed perception of what natural female bodies look like and what they  do.

Before you read anything else in this section about nipples, please read my post What You Need to Understand About ‘Free the Nipple.’

Typical/Atypical Nipples

As for nipples and areolas, really anything goes, and just about everything is ‘normal’ (click here for a gallery). Most humans have two, and they develop along the milk lines.

Basic biology: a nipple is actually the small, prominent bud that’s centered on an area of skin called the areola. Nipples don’t have just one hole like a plastic baby bottle, they have multiple holes (try manually spraying your milk and you’ll notice that it shoots out much like a sprinkler-head).

Basic biology lesson from Ken L. Smith at


Nipples really aren’t something to get so nip-picky (ha!) about. Keep in mind: even if your nipple may not be ‘perfect’ to you, it’s likely the only nipple your baby has ever known. He won’t be comparing. Rest assured, it’s perfect to him!

As Dr. Sears reminds, “Babies feed on areolas, not nipples.”

That said, sometimes nipples of certain types can pose breastfeeding problems, though it’s certainly not a guarantee.

Atypical nipple types:

  • Absent (athelia) – An extremely rare congenital anomaly in females and males alike, the absence of nipples and nipple pores is called athelia. It’s impossible to breastfeed unless only one nipple is missing.
  • Doubled/Bifurcated – Some women have more than one nipple on the areola (sometimes one appearing to be ‘split’ in two or more sections, or bifurcated). The extra nipple bud usually doesn’t give milk. It shouldn’t be expected to interfere with normal breastfeeding.
  • Folded – Appears as a slit with two folds that may rub together during nursing and cause a chafing sensation.
  • Flat – Causes of flattening of a normal nipple include IV fluids, water retention, and engorgement. Nipples that are always flat don’t protrude when stimulated (or only minimally). Babies have a hard time latching onto a flat nipple and often require extra help. Fortunately, many breastfeeders find that the nipple gets stretched out with continued nursings. (See “True Inverted” below for flat nipple treatments).
  • Long/Oversized – The Alpha Parent asks, “When a mother is blessed with nipples the size of dinner plates, can this interfere with her baby’s dining experience?” Read one mom’s story here. Then check out these guidelines to help when two big nipples become too big a problem.
  • Polythelia – Remember when we found out that our favorite Friend Chandler Bing had a third nipple? Technically, that’s called polythelia. Third nipples are actually not uncommon; they occur in 1 in 18 males and 1 in 50 females and are often mistaken for moles. As opposed to polymastia, milk glands cannot be present with the accessory nipple in the case of polythelia.
  • Pseudo-Inverted – Also known as ‘retractile’ or ‘umbilicated.’ They can be treated like common nipples because, though they appear inverted at rest, they do become erect with stimulation (unlike true inverted).
  • Retracted – This type is the opposite of pseudo-inverted: normal at rest, but inverts upon stimulation/pressure. Unlike the benign case of another inversion, a retracted nipple should be evaluated by a doctor as it might signal a cancerous malignancy or an underlying growth if the nipple also appears to have changed its direction/angle.
  • True Inverted – Depending on the severity of the inversion (or flat nipple), solutions include: breast pump, ‘breast sandwich,’ breast shields, the Hoffman technique, nipple formers, and the Niplette. Find out more here and here.

“[I]nverted nipples are mostly caused by adhesions which never opened up naturally during puberty resulting in abnormal nipples. During nursing there will be some pain as the nipples are pulled out, but just remember it is temporary and the nipples usually start to look normal after a while. Most of the time you will only have one inverted nipple. In this case, you will be able to feed baby on the ‘good side’ while you pump the other side…the more you breastfeed the larger your nipple will become and the more it will stand out.” – per

Infant Suckling: How Does it Work?

Ben, three years old. Photo Credit: Ana & Ivan Photography

Ben, three years old. Photo Credit: Ana & Ivan Photography


  • Chew Then Swallow – The popularity of purees went hand-in-hand (rather, spoon-handled-to-mouth) with the advent of bottles. Why? Because of the backwards way puree-fed babies learn to eat: they learn to swallow before they learn to chew. Doesn’t make much sense, does it? Breastfed babies (who don’t use bottles) learn to chew BEFORE swallowing, and typically have an easier transition to solid foods. From BfB: “When a baby being given a bottle swallows, the negative pressure created draws more milk into the baby’s mouth, meaning the baby has to swallow again to avoid choking. This is stressful for the baby, and babies will often display stress cues such as splayed fingers or toes, milk running out of the corner of the baby’s mouth, trying to turn their head away, or trying to push the bottle away.”
  • Developing Jaws – Babies who eat from the breast get the proper mechanics for the building and strengthening of maxillofacial and jaw muscles and bones, which results in broader, more well-developed jaws. The narrowed, less-developed jaws of a bottle-fed baby can affect the arrangement of adult teeth later on (crowded teeth; braces?).
  • “Comfort Zone” Latch Refresh your memory about latch basics and learn why it’s such a crucial factor in your comfort and your baby’s ability to transfer milk. This video provides an internal view of a baby’s mouth as he latches.
  • Pressing Tongue – The way a baby nurses is that s/he will lightly suckle (sometimes flutter nursing) briefly just to let down the milk, then when the milk is flowing freely s/he doesn’t really ‘suck’ but uses chewing motions with the tongue and jaw to push out the milk –- in essence, to eat (similar to how an older child or adult would eat a peach, or whatever). Remember that the milk reservoirs sit just behind the areola, so they must be compressed between the baby’s tongue and soft palate to draw out the milk. Here is an really excellent Powerpoint that shows illustrations demonstrating the position and action of the tongue during breastfeeding.
  • Covered Teeth – Because a baby’s tongue covers the gums, it’s normal for a baby’s milk teeth (baby teeth) to come in and not be felt by the mother. Sure, some babies try to bite for different reasons, but they are not nursing while doing this. A baby cannot physically bite and eat simultaneously. Read more about biting and baby teeth here.
Photo Credit: Ana & Ivan Photography

Photo Credit: Ana & Ivan Photography

In Human Breastfeeding is Not Automatic: Why That’s So and What it Means for Human Evolution, Anthony A. Volk writes (emphasis mine):

“[I]t appears that while infant primates have a natural suckling reflex, in many primate species, mothers require learning to be able to successfully nurse their infants. In this regard, primates are unlike other mammalian orders, who generally do not require learning to be able to successfully nurse their offspring. Amongst primates, the greater the primates’ intelligence (e.g., great apes compared to other primates), the greater the need for learning [how to breastfeed].

“The shape of the human breast typically translates into a different feeding action when compared to other mammals. While most mammals use negative suction to draw milk…it is believed that human infants primarily use positive pressure on the areola to express milk from the nipples. The positive pressure from within the mother’s breasts and negative suction in the infant’s mouth is of secondary importance…”



*The following is based on my experience nursing a less than 1.5 year old*

Well, when it doesn’t hurt or feel uncomfortable for a variety of possible reasons such as shallow latch or nipple infection, it feels pretty nice! Or, like nothing at all honestly.

Most of the time I forget there’s actually mouth action happening on my breast because what I’m feeling even more strongly is the connection between me and my child. I feel his eyes locked on my face even when I’m looking away. I feel his hands tug at my hair or caress my collarbone. I feel his warm body burrow up into my belly as if he knows that’s where his home once was for nine months.

I feel his calming wispy baby breaths on my skin. I feel his imaginative spirit as he nurses with the look of focused contemplation that reflects a lot of turning wheels, processing what’s happened around him earlier today. I feel his complete trust as he points around the room, silently requesting that I tell him all about each strange object in view.

I feel his arm hook around my neck to attempt the smallest yet biggest hug imaginable. I smell the grassy pheromones dewy and heavy in his sweaty hair. I hear his sighs, mews, belly laughs, disapprovals, and encouragements.

When I do notice the gentle tug-push sensation of his suckling, it reminds me of something I read in a breastfeeding book. It was described as how a cat cleans it’s human owner’s palm with its tongue. It’s kind of relaxing and pleasurable, like getting lost in a wistful memory; not rough enough to hurt and not soft enough to tickle; somewhat repetitive, almost to the point of annoyance if it goes on too long when you’re really not in the mood.

Of course, as a nursling ages, so does the mother, along with her re-balancing state of hormones, and her hard-working breasts (thankfully the milk itself is ageless). New feelings touch base at that time; they can be both good and bad but either way much different from those of newborn nursing yesteryear.

Keep reading: How Should Breastfeeding Make You Feel? and 10 Differences Between Nursing an Infant & Nursing a Toddler).