Lactation Hormones

Breast Hormones of Development and Lactation

Hormones and lactation (Lactation hormones)

Breast growth hormones Estrogen and Human Placental Lactogen work on the growth of the breast before pregnancy. Progesterone, Prolactin, and Oxytocin are all involved during pregnancy and lactation.



During pregnancy the levels of Estrogen are higher, these levels cause the growth of the breast tissue.

Human Placental Lactogen:

Also higher during pregnancy and stimulates the growth of the breast tissue, the nipples, and areola.


This hormone causes the breast tissue to multiply but inhibits milk production. After birth, progesterone levels drop, this triggers milk production.

newborn baby breastfeeding, breastfeeding hormones

Prolactin and cortisol:

Prolactin makes the cells differentiate to perform their own specific role. After birth, the alveoli produce milk because of Prolactin (this hormone is sent via the hypothalamus) Prolactin can only be created after exposure to Cortisol.

Prolactin levels vary according to:

  • Levels of Prolactin are higher at night.
  • Prolactin levels are at their highest until two months postpartum. They are also higher in women who breastfeed after this period. Once the mother weans, the levels drop again.
  • Prolactin levels increase if more milk is removed from the breast.
  • Women who smoke have lower Prolactin levels.
  • Stress and anxiety may decrease Prolactin levels.
  • High Prolactin levels are inclined to delay ovulation. 
  • Learn more about the delayed onset of breast milk


Functions of the lactation hormone Oxytocin:

  • It causes muscle contractions, which cause the muscles of the uterus to contract in labor. Oxytocin also helps the uterus return to its normal size after pregnancy.
  • Oxytocin is released when the nipples are stimulated, it causes the alveoli to contract, which squeezes the milk out into the duct system. This is called a let-down. A let-down happens a few times while breastfeeding.
  • Oxytocin has a calming effect. Women who breastfeed, have lower levels of stress hormone than non-breastfeeding women. 

Breast Anatomy and Lactation Hormones

Learn more about the anatomy of the human breast

Tracy Ann Behr, CBC, CLD (CBI)

Courses on hormones of lactation through Childbirth international

Join us facebook breastfeeding page