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How breastmilk is produced

How breastmilk is produced


When does breastmilk production begin?

The breast begins to prepare for lactation during early pregnancy.

It is important to note that pre-pregnancy breast size has no correlation to the amount of milk you may produce when your baby is born. It also has no correlation to the degree in which your breasts will grow and develop during pregnancy.

How does breastmilk come through the breast?

The breast is composed of primarily fatty tissue, but also contains milk producing glands - called lobules. These lobules are connected to the nipple by a network of pathways called milk ducts.

Milk production happens inside these lobules, which contain alveoli.

Alveoli are grape-like clusters of cells within the breast. Water and nutrients are removed from the bloodstream and used to synthesize breastmilk which is stored in the alveoli/lobules.

When baby is born and begins to breastfeed, the hormone oxytocin signals tiny muscle contractions in the lobules which push breastmilk out of the alveoli and down along the milk ducts. This is known as a “let down” or the milk ejection reflex.

What does a let down during breastfeeding feel like?

Not everyone will be able to feel a physical change during a milk let down.

But some mothers describe the sensation of let down as:

  • Tingling or electric sensation along the breast
  • Dull ache or tightening sensation of the breast
  • Milk leaking from one or both breasts
  • If breastfeeding soon after birth – uterine cramps, as oxytocin release helps to return the uterus to its pre-pregnancy state.

Can let down happen at random times?

If you have been breastfeeding for a while, you may have noticed a let down reflex can happen for other reasons. You may begin leaking when you hear another baby cry, when you see or think of your baby or when it’s the time your baby regularly feeds. 

This is due to the oxytocin release in your brain as a result of your physical and emotional connection to caring for your baby. As long as this oxytocin continues to be released, the milk ejection reflex will continue to provide milk for your baby.

 Written by Keryn Thompson, RM & IBCLC (L-301766)


Alex, A., Bhandary, E. and McGuire, K., 2020. Anatomy and Physiology of the Breast during Pregnancy and Lactation. Advances in Experimental Medicine and Biology, pp.3-7.

Gardner, H., Kent, J., Prime, D., Lai, C., Hartmann, P. and Geddes, D., 2017. Milk ejection patterns remain consistent during the first and second lactations. American Journal of Human Biology, 29(3).

Jonas, W. and Woodside, B., 2016. Physiological mechanisms, behavioral and psychological factors influencing the transfer of milk from mothers to their young. Hormones and Behavior, 77, pp.167-181.

Kent, J., Prime, D. and Garbin, C., 2012. Principles for Maintaining or Increasing Breast Milk Production. Journal of Obstetric, Gynecologic & Neonatal Nursing, 41(1), pp.114-121.

Neville, M., 2001. Anatomy and Physiology of Lactation. Pediatric Clinics of North America, 48(1), pp.13-34.

Sriraman, N., 2017. The Nuts and Bolts of Breastfeeding: Anatomy and Physiology of Lactation. Current Problems in Pediatric and Adolescent Health Care, 47(12), pp.305-310.

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