Your breasts will stage producing milk in increased volume 30 to 40 hours after you give birth and this stage is known Lactogenesis II. However, during the latter part of your pregnancy, your breasts do manufacture colostrums but the presence of progesterone does not allow milk to be secreted. Once you give birth, there is an abrupt drop in the levels of progesterone and estrogen, which leads to the production of milk or Lactogenesis II.

       Although production of copious amount of milk starts 30 to 40 hours after giving birth, most women do not feel an increase in breast fullness until 50 to 70 hours after giving birth. Lactogenesis I and II are hormonally driven and occur whether or not a woman is breast feeding her baby.

      Thereafter, the body changes to a different control system. Now it becomes a supply and demand process. When the baby drinks milk, the breasts become empty. This leads to further production of milk. Under normal circumstances, the breasts will continue to produce milk as long as milk removal continues. This said, hormones can still interfere with the supply of milk but their levels play a lesser role.

      Physiology behind lactation is rather simple. Here is a non-scientific explanation. For milk production to take place, a hormone called prolactin has to be present. On the walls of the milk producing cells of the alveoli, there are prolactin receptors that allow prolactin to be taken from the blood and stimulate the production of milk. When the breasts (alveoli) are full of milk, prolactin cannot enter the receptor sites and thus the rate of milk production decreases. As milk empties from the alveoli, prolactin receptors allow prolactin to pass through and the rate of milk production increases.

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