A good milk ejection reflex is a key factor for successful breastfeeding. A mother can produce milk, but if it is not removed, further production is inhibited (Lawrence and Lawrence, 2011c). Before this reflex is established, the baby can only suckle, or the woman can only express, small amounts of milk (1–10 ml) (Geddes, 2007). This is actually a complex process that depends on the functioning of the nervous, glandular, and endocrine systems. It is most easily inhibited by psychological blocks (Lawrence and Lawrence, 2011c).

The milk ejection reflex is a neuroendocrine reflex, most often triggered by nipple stimulation. Nerve impulses travel from the nipple to the magnocellular oxytocin neurons in the hypothalamus, causing oxytocin synthesis. This impulse then travels along axons to the capillary plexus of the neurohypophysis. From there, it is released in impulses into the bloodstream and travels to the breasts, where it causes the milk ejection reflex (Walshaw, 2010). When oxytocin reaches the breasts, it causes the contraction of myoepithelial cells surrounding the alveoli, thereby stimulating milk ejection into the milk ducts (Kent et al., 2010). This results in an increase in intraductal pressure and the dilation of the milk ducts. Both lead to an increased rate of milk flow (Geddes, 2007). According to Lawrence and Lawrence (2011c), the first contractions of myoepithelial cells appear within the first minute after the start of suckling. However, it often takes two full minutes or more for a complete response to occur. The milk ejection reflex occurs multiple times during a single feeding. It is estimated to occur up to nine times. The average number of reflexes during a single feeding is reported to be up to 2.5 times (Geddes, 2007). The pattern of pulsatile oxytocin release is crucial for ensuring normal milk flow (Walshaw, 2010). Mothers most often experience this moment as warmth or tingling in the breasts. Some even experience brief nausea or thirst (Kent et al., 2010). Most women feel the first milk ejection reflex, but only a few feel subsequent ones (Geddes, 2007). As Kent et al. (2010) state, mothers do not perceive approximately 30% of reflexes.

Other forms of mechanical stimulation to the nipples also have the same effect on the breasts and uterus. The milk ejection reflex is centrally inhibited by the following factors: cold, pain, and emotional stress. The reflex can be partially blocked by a larger amount of alcohol, which is presumed to prevent oxytocin secretion. Vaginal arousal is believed to stimulate this reflex. To help trigger the milk ejection reflex, prior manual expression of a small amount of milk, warm compresses, and gentle breast massage are helpful. The milk ejection reflex can cause a transient headache at the onset of milk flow. Nausea, associated with oxytocin release, may also occur (Lawrence and Lawrence, 2011c). It is important to ask whether these could be indicators of a higher risk for the development of D-MER in a breastfeeding mother. That is, whether a mother who experiences nausea or headaches during milk ejection is a candidate for developing D-MER throughout continued breastfeeding.