Your milk ejection reflex: what letdown feels like and how it works
What does a letdown feel like?
Women experience letdowns in many different ways - since normal is a highly diverse human condition! Most of the time, we don't feel letdowns at all.
Milk ejections can feel tingly or tight, like a hot prickling sensation in the breasts, or like 'pins and needles'. Some women might describe a feeling of release in their breasts. The sensation might also have a sharp edge to it. For some, milk ejection may feel weird and uncomfortable, or may even be experienced as pain.
This is not the kind of pain that warns of physical danger though, so if you are one of those who experience letdown as unpleasant or painful, it helps to remember that the glands are simply contracting to deliver milk, and that nothing bad is going on. (The condition of Dysphoric Milk Ejection Reflex is different again, and requires special attention and help from your health professionals.)
Quite often women feel thirsty with milk ejection. In the early days after the birth, your womb may contract uncomfortably with letdowns, though this massages the womb and helps restore it to a non-pregnant state.
When your breasts are working at their hardest to make milk, there can seem to be a randomness to letdowns. You'll notice a tingling sensation and then a leak into your T-shirt if you're not wearing a bra, or you'll notice the warmth of breast pads, filling, just when you're minding your own business or getting tasks done. Milk ejection might occur in response to breast fullness, it might be a spontaneous release of milk, or it might be a physical response to sights and sounds that remind you of your baby.
Many women sense the first letdown in a breastfeed, but don't know that they are having subsequent milk ejections. Some women don't feel letdowns, ever, though they are having them, and this too is normal.
How do letdowns happen?
Your letdowns or milk ejections are essential for breastfeeding and your ongoing production of milk. Repeated letdowns are the only way milk can be consistently and effectively transferred out of your milk glands, which happens in tandem with the vacuum generated when your baby suckles or with the pump if you're expressing.
The letdown, or milk ejection reflex, is a coordinated release of milk from your alveolar glands into the milk ducts. When your baby first comes onto the breast, she might notice that she starts suckling with rapid jaw drops, before slowing to something closer to suck-swallow-suck-swallow or suck-suck-suck-swallow suck-suck-suck-swallow once your milk starts to flow.
There are three steps to a milk letdown.
Step 1: mechanical and touch stimulation of the nerve receptors in your nipple
Letdown most commonly and very reliably occurs in response to mechanical stimulation of the sensory nerve endings in your nipple. Your nipple is extensively innervated. (A variety of sensory input (tactile, auditory and visual) also trigger your baby's breastfeeding reflexes, so that your little one comes on, creates a seal, and drops her jaw to create the vacuum.)
Most commonly, a letdown is stimulated by the nerve impulses which result when your baby is rhythmically suckling at the breast, providing both intermittent mechanical pressure sensations, and the sensory bath of baby's warm little tongue and mouth bathing your nipple.
Step 2: signals travel to your hypothalamus then to your posterior pituitary, which releases the hormone oxytocin
The nerve endings in your nipple send impulses which travel into your brain, landing in your hypothalamus. The hypothalamus speaks to your pituitary gland, which releases the hormone oxytocin into your blood stream.
Sometimes you might also notice your body responding to what you hear or see or imagine: oxytocin is also released from the posterior pituitary when you think of your baby, or hear your baby cry, or when your breast is full.
Step 3: a surge of oxytocin travels to your breasts, where it causes the myoepithelial cells to contract
Oxytocin is then transported to your breasts, where it has two quite opposite effects.
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When oxytocin binds to the star-like myoepithelial cells of the alveoli, those smooth muscle cells contracts, the glands contract, and milk is pressed into your ducts. The alveoli lose a third of their surface area, and become irregularly and randomly scrunched up, expelling milk. deformation as a result of deformation to the alveolar structure in response to repetitive basal cell contractions with oxytocin stimulation. It is a random The force is repetitive and random, unpredictable. Lactocytes are compressed and stretched, repetitively and randomly. This means that the pressure inside the lactiferous ducts increase, the ducts dilate, and milk flows.
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When oxytocin binds to receptors on the star-like myoepithelial cells of the ducts, those smooth muscle cells contracts- and the ducts widen and shorten. This is because alveoli and ductal myoepithelial cells are configured differently. When milk is pressed from the alveoli into the milk ducts it flows along easily, with minimal resistance, because the ducts have widened, not just in response to the positive pressure of the milk, but also in response to the myoepithelial cell contractions.
Letdowns are like waves breaking slowly along a beach
Letdowns are like waves breaking along a beach. Some waves are big, some are small. They don't roll in completely predictably, as if they were generated by a machine!
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Even in response to the one single oxytocin surge, milk ejection rolls out irregularly across your breast. The timing of the contraction response is highly variable.
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Fuller alveoli eject milk sooner in response to the oxytocin surge than those which happen to be less full - and the amount of milk in the alveoli is highly variable at any one time, both within the lobules, and throughout the breast. Alveoli are always in different phases of milk secretion. Not all alveoli are fully developed within a breast, and there are non-functioning ducts too within a lactating breast.
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Alveoli are not uniformly contracted or dilated in response to an oxytocin surge: some are contracted, some are dilated in any one neighbourhood or cluster.
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Some backward flow of milk during milk ejection fills up ducts that don't have milk in them.
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Contraction of the myoepithelial cells surrounding alveoli that have been partially emptied may result in lower intraductal pressure and smaller duct dilation.
Milk ejection definitely doesn't function like a piston in a machine, which predictably pulses out standard amounts of milk! Milk duct dilation and milk flow are irregular and asynchronous.
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Recommended resources
Do you have Dysphoric Milk Ejection Reflex?
Two stories about maternal stress and letdown worries
Does stress affect your breast milk letdowns or supply?
Your milk ejection reflex: what letdown feels like and how it works
Why your milk ejections are resilient and very difficult to disrupt
Busting myths about your letdown or milk ejection reflex
Selected references
Gardner H, Kent JC, Prime DK, Lai C-T, Hartmann PE, Geddes DT. Milk ejection patterns remain consistent during the first and second lactations. American Journal of Human Biology. 2017;29:e22960.
Geddes DT. Inside the lactating breast: the latest anatomic research. Journal of Midwifery and Women's Health. 2007;52(6):556-563.
Ramsay DT, Kent JC, Owens RA, Hartmann PE. Ultrasound imaging of milk ejection in the breast of lactating women. Pediatics. 2004;113:361-367.
Ramsay DT, Kent JC, Hartmann RA, Hartmann PE. Anatomy of the lactating human breast redefined with ultrasound imaging. Journal of Anatomy. 2005;206:525-534.
Ramsay DT, Mitoulas LR, Kent JC, Cregan MD, Doherty DA, Larsson M, et al. Milk flow rates can be used to identify and investigate milk ejection in women expressing breast milk using an electric pump. Breastfeeding Medicine. 2006;1(1):14-23.
Prime DK, Geddes DT, Hepworth AR, Trengove NJ, Hartmann PE. Comparison of the patterns of milk ejection during repeated breast expression sessions in women. Breastfeeding Medicine. 2011;6(4):183-190.
Stewart TA, Hughes K, Stevenson AJ, Marino N, Ju AL, Morehead M, et al. Mammary mechanobiology - investigating roles for mechanically activated ion channels in lactation and involution. Journal of Cell Science. 2021;134:doi:10.124/jcs.248849.
Woolridge MW. The 'anatomy' of infant sucking. Midwifery. 1986;2:164-171.
between 72 and 120 sucks/min, to 6 sucks/minutes