The Biology of Milk Supply: Hormones, Feedback & Autocrine Control

Milk Supply

Human milk production is one of the most remarkable biological systems in the body — dynamic, responsive, and beautifully designed to adapt to both the baby’s needs and the mother’s environment. Yet many parents are told simplistic phrases like “it’s just supply and demand,” without understanding how supply is regulated or what truly influences it.

By understanding the hormones involved in early lactation, the local breast-based feedback system that takes over later on, and the remarkable mechanisms that calibrate supply from feed to feed, parents can feel more confident in navigating and understanding their own feeding journey. At Bubba & Me our approach blends solid evidence with truly nurturing care. Our breastfeeding support in Tunbridge Wells and Sevenoaks is designed to help parents feel informed, supported, and confidently connected to their feeding journey.

This article explores the three core pillars of milk production:

• Hormonal regulation (prolactin, oxytocin)

• Autocrine control (the breast regulating its own output)

• Feedback mechanisms including the fascinating Feedback Inhibitor of Lactation (FIL)

Let’s break down how your milk supply actually works — and why confidence grows when knowledge does.

The Hormonal Blueprint: Prolactin & Oxytocin

In the early days after birth, milk production is primarily driven by hormones. Two play leading roles: prolactin, which builds supply, and oxytocin, which releases it. Their interaction creates the foundation for a healthy milk supply long-term.

Prolactin: Building the Milk Factory

Prolactin is released from the pituitary gland in response to nipple stimulation. Every feed — and crucially, every effective feed — creates a surge of prolactin in the bloodstream. These pulses are especially strong at night, which is why overnight feeding is so powerful for long-term supply.

Prolactin tells the milk-making cells (the lactocytes) to synthesise milk. The more often milk is removed, the more frequently prolactin rises, and the more robust the overall supply becomes. It’s a clever and responsive system — and one that is highly individualised from parent to parent and even from breast to breast.

Oxytocin: The Release Mechanism

If prolactin builds the milk, oxytocin allows it to flow. When your baby latches, oxytocin causes tiny muscle cells around the alveoli to contract, pushing milk through the ducts and out to the nipple — a process known as the let-down reflex.

Oxytocin is deeply influenced by the environment. Calm, safety, warmth, dim lighting, soft voices, skin-to-skin — these conditions help oxytocin flow. Stress, pain or feeling observed can temporarily suppress it. This is why breastfeeding support is not only about latch or technique; it’s also about the space, the nervous system, and feeling truly supported.

For parents in Kent, our clinic offers gentle, person-centred breastfeeding support in Tunbridge Wells and Sevenoaks helping create the right conditions for oxytocin to do its work.

Autocrine Control: When the Breast Takes the Lead

Around day 3–4 postpartum, something extraordinary happens. Control of milk production shifts from being mostly hormonal to being mostly local. This is called autocrine control, and it’s where milk production becomes exceptionally adaptive.

Unlike hormonal regulation, autocrine control responds within each breast individually. This is why a baby who prefers one side will stimulate more supply on that side alone. The system is dependent on one factor:

how much milk is removed, and how consistently.

When milk is removed frequently, the breast speeds up production. When milk sits in the breast for longer periods, production naturally slows. It’s not a moral failing, a personal flaw, or a sign of “your body not making enough” — it’s simply the biology of the breast responding to perceived demand.

This is also why support early on can make such a meaningful difference. Understanding how to optimise the feeding pattern, how to recognise effective removal, and how to manage one-sided preference or inefficient feeding is essential.

The Feedback Inhibitor of Lactation (FIL): The Breast’s Internal Regulator

One of the most fascinating components of milk supply physiology is a small whey protein called the Feedback Inhibitor of Lactation (FIL). FIL is found within breastmilk itself, and its job is simple but powerful:

to slow down milk production when the breast becomes too full.

Here’s how it works:

• When the breast is full, FIL accumulates.

• FIL attaches to receptors in the lactocytes.

• Those receptors tell the cells to reduce milk synthesis.

• Milk production slows until demand increases again.

When milk is removed frequently, FIL levels remain low and supply stays high. When feeds are skipped or milk is not removed effectively (e.g., shallow latch, fast supplementation, tight clothing compressing the ducts), FIL levels rise and signal the breast to reduce production.

This system is elegant, intelligent, and responsive. It ensures that supply closely tracks what your baby actually needs — not what a schedule dictates or what old myths suggest.

Why Understanding the Biology Matters

Parents often feel anxious about supply, but when we explain these systems — prolactin surges, oxytocin rhythms, autocrine regulation and FIL — a shift happens. The feeding journey begins to feel less mysterious, less stressful, and more grounded in understanding.

This is the heart of our approach at The Bubba & Me Club: combining science-led antenatal and postnatal education with nurturing, individualised support. If you’re seeking guidance with latch, positioning, oversupply, low supply, pumping, tongue tie questions or simply reassurance, we offer:

• Breastfeeding support in Tunbridge Wells

• Breastfeeding support in Sevenoaks

Final Thoughts

Milk supply is not random. It is regulated by a precise and intelligent blend of hormones, feedback loops, and breast-based signalling systems. When parents understand the biology, they feel more empowered — and more supported — in whatever feeding journey unfolds.

If you’d like personalised guidance or reassurance, our clinic would love to support you. Your feeding journey matters — and you deserve care that honours both the science and the lived experience of early parenthood.