Do Nipples Have Holes? How Milk Exits the Body

Nipples do have holes, and more than most people expect. The surface of each nipple contains multiple tiny openings called ductal orifices, typically between five and nine on a single nipple, though the range extends from as few as two to as many as sixteen. These openings are the endpoints of a branching network of ducts that runs deep into the breast tissue, and they are the exit points through which milk leaves the body during breastfeeding or pumping. The story of how milk actually travels from deep in the breast to those surface openings involves hormones, specialized muscle-like cells, and even suction from the infant’s mouth working together.

How Many Openings Does a Nipple Have?

If you look at a nipple closely, you won’t see one central hole. Instead, the surface is dotted with several tiny pores, each one connected to its own independent duct system. A study of 95 lactating women found that the average number of ductal orifices across both nipples was about eight per nipple, with no meaningful difference between the left and right sides.¹ A separate anatomical study reported that over 90 percent of nipples examined had between five and nine orifices, usually arranged in a central cluster and a surrounding ring.²

Those numbers refer to openings you can identify at the surface, but beneath each opening the picture branches further. Three-dimensional reconstructions of nipple tissue have shown that a single nipple can contain more than 20 ducts, with one detailed reconstruction finding 29 ducts emerging from just 15 surface orifices.³ So some ducts share an exit point, merging just before they reach the skin. Each orifice feeds into its own separate ductal system that doesn’t connect to the neighboring ones, which means that if one duct gets blocked, the others can still function independently.²

The Duct Network Underneath

For a long time, anatomy textbooks described the breast’s internal plumbing in a way that turned out to be oversimplified. The classic illustration showed milk collecting in large balloon-like reservoirs called lactiferous sinuses, sitting right behind the areola, waiting to be squeezed out. Ultrasound imaging of lactating women has overturned that picture. Researchers scanning breasts during active milk production found that the “typical” sac-like sinuses simply weren’t there. Ducts did widen at branch points, but the large pooling reservoirs shown in older diagrams did not appear.⁴

Instead, the ducts branch early and extensively, splitting apart very close to the nipple and fanning out into the deeper breast tissue. The portions of the duct that do expand and store milk are scattered throughout the ductal system rather than concentrated in one spot right behind the nipple.⁵ Just beneath the skin surface, the ducts are very narrow, gradually widening as they run deeper into the nipple and toward the body of the breast.³ This matters practically because it means there’s no single reservoir to “empty.” Milk has to be actively moved through a complex tree of channels to reach those surface openings.

How Milk Gets Pushed to the Surface

Milk doesn’t simply drain out of the breast by gravity. The process depends on a hormone called oxytocin, which the pituitary gland releases in response to stimulation like a baby suckling, skin-to-skin contact, or even hearing a baby cry. Oxytocin travels through the bloodstream and reaches the breast, where it triggers tiny muscle-like cells wrapped around the milk-producing sacs deep in the tissue. These cells, called myoepithelial cells, squeeze the sacs and push milk into the primary ducts.⁶ That squeezing force is what drives the milk from the interior of the breast toward the nipple openings.

The contraction of these cells is not optional or minor. Research in mice genetically lacking the key protein that gives myoepithelial cells their contractile ability showed that milk ejection was severely impaired without it.⁷ In practical terms, this is why stress or anxiety can interfere with breastfeeding. Stress hormones can suppress oxytocin release, and without oxytocin the myoepithelial cells don’t contract, leaving milk sitting in the glands even though it’s been produced. Many people experience this as the breast feeling full but milk not flowing well.

What the Baby’s Mouth Actually Does

The hormonal push from inside the breast is only half the equation. The infant’s mouth creates a vacuum that actively pulls milk out through the nipple openings. Ultrasound imaging of breastfeeding infants has shown that milk flow from the nipple into the baby’s mouth coincides with both the downward movement of the infant’s tongue and the point of peak vacuum inside the mouth. That peak vacuum was measured at roughly negative 145 mmHg, a surprisingly strong suction force generated by a newborn.⁸

This finding changed the understanding of breastfeeding mechanics. Earlier models focused heavily on the baby’s jaw compressing the breast tissue, essentially squeezing milk out. The ultrasound evidence pointed instead to vacuum as the major force pulling milk from the ducts. The tongue’s rhythmic motion creates a wave that lowers pressure inside the mouth, drawing milk through the orifices and into the oral cavity. It’s a cooperative process: oxytocin-driven contractions push milk forward through the ducts, and the infant’s suction pulls it the rest of the way out.

The Areola’s Own Separate Openings

The nipple orifices aren’t the only openings on the breast’s surface. The darker ring of skin surrounding the nipple, the areola, is dotted with small raised bumps. These are Montgomery glands, and they have their own pores. Montgomery glands secrete a mixture of oily and waxy substances that lubricate the nipple and areola, which helps protect the skin during breastfeeding. But their role goes beyond simple moisturizing.

Research has shown that the scent of these secretions is powerfully attractive to newborns. When exposed to the odor of areolar secretions from lactating women, infants increased their breathing rate and showed appetitive oral responses like mouth opening and tongue movements. These responses appeared to develop independently of any direct experience with the breast, meaning even newborns who had never breastfed reacted to the scent.⁹ The volatile compounds in these secretions appear to help guide the newborn to the nipple and trigger feeding behavior, playing a role in milk transfer, bonding, and even survival in the first hours of life.

When the Openings Get Blocked

Because the ductal orifices are so small, they’re vulnerable to obstruction. One common problem during breastfeeding is a nipple bleb, a small blister-like lesion that forms directly over a duct opening. Blebs are fibrinous (made of a clot-like material), and they can seal off a single orifice, blocking milk from exiting through that duct. They often appear as a white or yellowish dot on the nipple tip and can be quite painful. Research suggests that blebs are the surface expression of deeper ductal plugging, and they can occur alongside bacterial imbalance in the breast and even excessive milk production.¹⁰

On the more severe end, repeated trauma to the nipple from pumping, a poor latch, or manual expression can trigger an inflammatory response at the ductal opening. This inflammation can lead to scarring and narrowing of the duct, and in some cases, small calcified stones can form inside the duct itself. Researchers have proposed that this process sits on a spectrum: a mild bleb at one end and a fully obstructing stone at the other, with the underlying mechanism involving a combination of surface trauma and internal duct inflammation that together create the conditions for a blockage to develop.¹¹ Since each duct system is independent, a blockage in one doesn’t necessarily stop milk from flowing through the others, but it can cause localized pain, swelling, and, if left unresolved, mastitis.

Traffic Goes Both Ways

One of the more surprising discoveries about nipple openings is that they aren’t strictly one-way exits. During breastfeeding, small amounts of milk can flow backward from the infant’s mouth back into the breast through the ductal orifices.¹² This retrograde flow carries bacteria from the baby’s mouth and skin into the duct system.¹³

This isn’t necessarily a bad thing. The breast has its own microbiome, a community of bacteria living inside the ducts, and retrograde flow from the infant’s mouth is thought to be one of the ways that community gets established and maintained. The exchange goes in both directions: the infant receives bacteria through the milk, and the breast receives bacteria from the infant’s mouth. This back-and-forth likely contributes to the specific bacterial mix found in human milk, which differs from what’s found on the surrounding skin. However, the same pathway can also introduce problematic bacteria, which may contribute to mastitis or duct infections when the balance is disrupted. Breast pumps may create similar retrograde effects, which is one reason pump hygiene matters.

Inverted Nipples and Duct Anatomy

Not everyone’s nipple anatomy looks the same. Inverted nipples, where the nipple retracts inward rather than protruding, are a common variation. They occur because short or tight bands of connective tissue pull the nipple inward, and in some cases the ducts themselves are shorter than average. An inverted nipple still has the same ductal orifices, but because the nipple sits flush with or below the areolar surface, an infant may have difficulty latching and creating the vacuum needed to extract milk.¹⁴

Surgical correction is possible, but the challenge is that traditional procedures risk cutting through the lactiferous ducts, which would permanently close off some of those orifices and potentially reduce or eliminate the ability to breastfeed. Newer techniques aim to release the connective tissue pulling the nipple inward while preserving as many ducts as possible. The degree of inversion varies: mild cases may self-correct with stimulation or suction devices, while more severe grades may require surgical intervention. For breastfeeding purposes, the functional question isn’t whether the openings exist but whether the nipple can protrude enough for the infant to latch and create effective suction.

What Happens to the Ducts After Breast Surgery

Breast reduction surgery removes tissue from the breast, and the question of whether the remaining ducts can still carry milk to the nipple openings is a genuine concern for people planning future breastfeeding. The answer is more encouraging than many expect. A recent study found that the ability to breastfeed was not significantly affected by a history of breast reduction, regardless of the specific surgical technique used or the amount of tissue removed.¹⁵

That said, outcomes do vary by technique. An older study comparing different approaches found that the best breastfeeding rates came from techniques that preserved the connection between the nipple-areola complex and the underlying glandular tissue. Among those methods, about 61 percent of patients who had a superior pedicle technique went on to breastfeed, compared with around 44 to 55 percent for other approaches.¹⁶ The critical factor is whether the surgeon can maintain blood supply and nerve sensation to the nipple while sparing as many ducts and milk-producing lobules as possible. When the nipple is completely detached and reattached during surgery (a “free nipple graft”), the ducts are severed entirely, and breastfeeding through those orifices becomes unlikely.

Do Male Nipples Have the Same Openings?

Male and female nipples start out with the same embryonic anatomy. During fetal development, the basic ductal structures form before sex hormones diverge, which is why men have nipples at all. In adult men, rudimentary ducts still exist beneath the nipple surface, and the same orifices are present, though the duct system is minimal and the milk-producing lobules never fully develop under normal hormonal conditions.

Under unusual circumstances, however, male breast tissue can actually produce milk. A documented case of a 27-year-old man with abnormally high prolactin levels showed that his breast secretion contained lactose, alpha-lactalbumin, and lactoferrin at concentrations within the normal range of colostrum and milk from lactating women.¹⁷ The hormonal environment was the only thing that differed from typical female lactation; the basic plumbing was already there. Certain medications and medical conditions that raise prolactin levels can trigger this, though it’s rare.

How Breast Pumps Work With Nipple Anatomy

Breast pumps are designed to mimic the two forces that drive milk out during breastfeeding: the internal push from oxytocin-triggered contractions and the external pull from suction. Most pumps rely primarily on vacuum, cycling between higher and lower suction to simulate the rhythmic action of an infant’s mouth. But research has shown that vacuum alone doesn’t capture the full picture.

Adding a compression component to the vacuum cycle increased the volume of milk ejected by roughly 10 to 46 percent compared to vacuum alone, with average milk output split about 60/40 in favor of the combined approach.¹⁸ This aligns with what we know about the duct network: since milk-storing portions are distributed throughout the breast rather than pooled in a single spot near the nipple, gentle compression helps move milk from those scattered reservoirs into the ducts where vacuum can draw it out through the orifices. Some newer pump designs incorporate this finding, alternating compression and suction in patterns meant to better replicate what an infant’s mouth does naturally.

Mammals That Don’t Have Nipples at All

If the idea of multiple nipple holes seems like an odd design, consider that some mammals skip nipples entirely. Monotremes, the group that includes the platypus and echidna, produce milk but have no nipples. Instead, milk seeps out through a patch of skin containing dense clusters of glands. Young monotremes lap or suck milk directly from the mother’s fur and skin surface. Researchers have proposed that this nipple-less arrangement may reflect an ancient structure that originally evolved to provide moisture and antimicrobial compounds to permeable eggs, long before it became a full milk-delivery system.¹⁹

The mammary gland itself is thought to have evolved from a combination of skin glands. Among the candidates that researchers have considered as possible ancestors, the best evidence points to a hybrid origin, with mammary glands sharing features of both apocrine glands (which secrete into hair follicles) and sebaceous glands (which produce oily skin secretions).²⁰ The nipple, with its concentrated bundle of duct openings, appears to be a later evolutionary refinement that made milk delivery more efficient. Instead of milk oozing out across a broad skin patch, the nipple channels it through a small number of discrete exit points that an infant can latch onto, creating the vacuum seal that drives effective feeding. From a design perspective, the multiple-hole arrangement makes more sense than a single opening: it provides redundancy if one duct gets blocked and allows milk to flow from several independent duct systems simultaneously.