There are different shapes of nipples out there. Some are flat; others are inverted while some protrude outwards away from the chest.
For women who belong to the former, breastfeeding is a little more complicated and they continually look for how to make their flat nipples stick out for breastfeeding. Some belong to neither group because their nipples fall in between.
Flat nipples lay with the areolas and the surrounding skin of the breast. Sometimes women confuse flat nipples with “sleeping” nipples, but that is not the case. The latter appear flat, but when stimulated by cold or sexual excitement, it becomes erect. The former don’t respond to cold or sexual stimulation.
The shape of the nipples is also influenced by the amount of fat in the breast, how long the milk duct is, and the number of connective tissues under the nipples. These factors determine if your nipples protrude, stay flat, or becomes inverted.