Key takeaways: After the first few days, milk production is driven mostly by how often and how well milk is removed. Emptier breasts make milk faster. Breast storage capacity varies between people, which is why some need to feed more often than others. Frequent, effective milk removal is the main way to build and keep supply.
Understanding how milk supply works can help you feel more confident and know what to do if your supply needs a boost.
Stage One: Hormones Start It
During pregnancy, the breasts prepare to make milk. After birth, when the placenta is delivered, progesterone falls. This triggers the larger volume of milk to come in, usually within 2 to 3 days (often called “milk coming in”). This first stage is driven mostly by hormones.
Stage Two: Milk Removal Keeps It Going
Within the first weeks, production shifts to being controlled mostly locally, in each breast, by milk removal.
- When milk is removed often and well, the breast makes more.
- When milk stays in the breast, a protein in milk (called feedback inhibitor of lactation) and pressure in the breast signal it to slow down.
- This is why each breast can make a different amount.
Prolactin and Oxytocin
- Prolactin supports milk production. Levels rise with feeding and nipple stimulation, and are higher at night.
- Oxytocin causes the letdown (milk ejection reflex), squeezing milk out of the milk-making cells. Stress, pain, and fatigue can slow letdown, while relaxation and skin-to-skin can help.
Emptier Breasts Make Milk Faster
Research by Hartmann and colleagues found that milk is made faster when the breast is emptier and slower when it’s fuller. Breasts are never truly “empty,” since milk is made continuously.
Breast Storage Capacity
Storage capacity is the amount of milk your breasts can hold between feeds. It varies widely and isn’t related to breast size.
- Larger storage capacity: may allow longer gaps between feeds while keeping supply.
- Smaller storage capacity: can still make plenty of milk in 24 hours but may need more frequent feeds.
Both can fully feed a baby.
What Helps Build or Protect Supply
- Feed early and often, at least 8 to 12 times in 24 hours in the early weeks.
- Make sure your baby has a good latch and transfers milk well.
- Use breast compressions and offer both sides.
- Avoid long gaps, especially early on.
- Add pumping or hand expression if your baby isn’t removing milk well or you’re separated.
- Avoid supplements you don’t need, which can mean less milk removal.
What Can Reduce Supply
- Infrequent feeds or long stretches without milk removal.
- Ineffective milk transfer (latch problems, tongue-tie, a sleepy baby).
- Some medications, such as estrogen-containing birth control and pseudoephedrine.
- Some medical conditions, such as retained placenta, thyroid disorders, and insufficient glandular tissue.
Talk to an IBCLC or your doctor if: your baby isn’t gaining well, has few wet diapers, or you’re worried about supply.
The Bottom Line
Milk supply runs on removal. Feed often and effectively, and get help early if something seems off.
Want more support for your baby’s first year? My book, From First Breath to First Birthday, is available on Amazon.
Sources
- Daly SE, Owens RA, Hartmann PE. The short-term synthesis and infant-regulated removal of milk in lactating women. Exp Physiol. 1993;78(2):209-220.
- Kent JC, Mitoulas LR, Cregan MD, et al. Volume and frequency of breastfeedings and fat content of breast milk throughout the day. Pediatrics. 2006;117(3):e387-e395.
- Kent JC, Gardner H, Geddes DT. Breastmilk production in the first 4 weeks after birth of term infants. Nutrients. 2016;8(12):756.
- Lawrence RA, Lawrence RM. Breastfeeding: A Guide for the Medical Profession. 9th ed. Elsevier; 2022.
This article is for general education and is not a substitute for individualized medical advice. Always talk with your baby’s health care provider or your own provider about your specific situation. If you think your baby or you may have a medical emergency, call 911.
