Your milk ejections are resilient and hard to disrupt

Your milk ejection reflex is resilient and not easily disrupted

You might have heard that you need to keep your letdowns working well by developing a routine around feeding, by using relaxation exercises, by applying warmth to your breast, by avoiding feeling self-conscious with others looking on, or by using distraction methods. These recommendations misunderstand how letdowns work, and can cause you a lot of unnecessary worry! It's awful to be told that your mental state or your emotions are disrupting the lovely, easy breastfeeding relationship you want to have with your little one, and there is no biological basis to this claim. However, if you are consistently experiencing stress or distress, this matters. Please consider cultivating a practice of self-compassion, and reaching out for support.

You might have been told that your baby isn't getting enough milk because your letdown isn't working properly. (It's true that if milk isn't being removed from your breasts often enough, repeated experiences of rising pressure in the milk glands will quickly dial down your supply, but this is different to your letdown 'not working'. There's an article on busting letdown myths elsewhere.)

Milk ejection is a classical neurohormonal reflex in response to mechanical stimulation of the nipple, hardwired and very difficult to disrupt.
Milk ejection is not a conditioned reflex, despite what you hear. Your milk ejection reflex has been hardwired through 310 million years of mammalian genetic encoding, and you can trust it.
Letdowns are outside our mental or emotional control, and are remarkably robust.
We don’t have to worry about letdowns in the same way we don’t have to worry about getting the acidity of our stomach's acid secretion right when we're eating. It looks after itself once we start eating.

If your baby breastfeeds with a good stable position and no breast tissue drag, if you make frequent flexible offers of the breast (and other breastfeeding problems have been sorted out), then over a 24-hour period - regardless of how many letdowns occur in any particular time at the breast - your baby will transfer the milk he needs.

Your breast and your baby don't always transfer milk every time she comes on

A healthy breastfed baby who is gaining weight perfectly well doesn't always transfer milk in a breastfeed.
But even when there isn't much to transfer, your ducts intermittently dilate if your baby is suckling. Letdowns happen even when there isn't much milk to let down (which is normal sometimes). What matters for your supply is that your baby develops flexible and frequent patterns of suckling over a 24-hour period. Frequent flexible feeds offer more opportunities for letdown. These may not be felt letdowns, and you might not see baby taking frequent fast swallows, but there will still be milk.
It doesn't matter how long your baby feeds for - the number of milk ejections during a breastfeed is the only factor that relates to how much milk your baby swallows in that breastfeed.
Some women have milk ejections in quick succession, other women have milk ejections which are much more spaced out. Your rate of milk ejections is unique to you, and doesn't change.
A fuller breast does have more vigorous letdowns, because it contains a greater volume of milk compared to a less full breast. But breast fullness is not a reliable sign of how much milk you're producing. There's no evidence to suggest that some women have stronger letdowns overall than others.

Your pattern of milk ejections is stable and unique to you

Depending on how long your baby is at your breast, you'll usually have multiple milk ejections - but the range of normal is wide.

Milk ejection patterns and volumes are highly variable between women but also uniquely programmed for each woman, with remarkable consistency over time, whether you are pumping or breastfeeding.
The time it takes for you to have a letdown, the length of your letdowns, and the number of letdowns you have within a period of time have been found to remain consistent throughout the first nine months of a breastfeeding journey. If you have another pregnancy, your milk ejection pattern stays more or less the same.
Milk ejection patterns are not particularly influenced by the baby, despite what you hear, but they do seem to be influenced by oxytocin and the genetically determined number of oxytocin receptors that you have in your glandular tissue and ducts.
The amount of oxytocin released at each milk ejection is the same within the one woman, although the volume of milk released by each milk ejection is highly variable and also depends on how much milk that has already been removed from the breast over the preceding hours.

Will synthetic oxytocin increase the amount of milk my baby drinks?

Sometimes women are advised to use oxytocin nasal spray to help with your letdowns. However ongoing exposure to synthetic oxytocin progressively desensitises oxytocin receptors and is not beneficial for release of milk overall. There is no role for oxytocin nasal sprays when you have breastfeeding problems.

Your milk ducts dilate up with a letdown

How widely do your milk ducts open up with letdown and is this variable?

The amount by which your unique milk ducts dilate during a milk ejection stays constant. The diameter of your ductal dilations doesn't relate to

How much milk you are producing in a 24 hour period
Your baby's milk intake
The amount of time your baby is suckling prior to the milk ejection
Time of the last breastfeed
How old your baby is
Whether it's your first, second or other child.

How long do ductal dilations last for and how often do they occur?

Each mother's milk ejection profile is innate and minimally influenced by infant characteristics - timing, duration, number of milk ejections.
Duration of ductal dilation is similar for all milk ejections, breastfeeds and mothers.
There is a minimum latency period of 45 seconds between milk ejections.
A large number of milk ejections can occur in a short period of time.
Each woman releases same amount of oxytocin at each milk ejection, though the amount varies between mothers.

Although your milk ducts are not a storage system, there is usually some residual milk in your ducts

Human milk ducts don't have sinuses or store much milk, unlike cows who hold substantial volumes of milk in cisterns in their udders.
However, the vacuum your baby generates with sucking between letdowns acts to draws out some milk. And remember, there are often multiple low-volume letdowns that you can't feel that continue to give the baby some luscious creamy milk, even if your baby's pattern is suck-suck-suck-suck-suck-suck-suck-suck-suck-suck-suck-swallow!

Recommended resources

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

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.

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.

Uvnäs Moberg K, Ekström-Bergström A, Buckley S, Massarotti C, Pajalic Z, Luegmair K, Kotlowska A, Lengler L, Olza I, Grylka-Baeschlin S, Leahy-Warren P, Hadjigeorgiu E, Villarmea S, Dencker A. Maternal plasma levels of oxytocin during breastfeeding-A systematic review. PLoS One. 2020 Aug 5;15(8):e0235806. doi: 10.1371/journal.pone.0235806. PMID: 32756565; PMCID: PMC7406087.

Woolridge MW. The 'anatomy' of infant sucking. Midwifery. 1986;2:164-171.