As many as 2 percent of American women have at least one inverted nipple, according to Southern California Nipple and Areola Correction. Most women with an inverted nipple were born with a congenital defect, inherited at birth. Three things can cause inverted nipples after a female is born: not enough skin at the base of the nipple, constricted milk ducts and scarring of the milk ducts due to breastfeeding. Some nipples remain inverted after breastfeeding while others return to a normal position.
About one in three mothers experience some degree of inversion during their pregnancies, according to Breastfeeding Basics, but only 10 percent of mothers still will have an inverted nipple by the time the baby is born. These women will experience a decreasing incidence of nipple inversion with each subsequent pregnancy.
Breastfeeding your baby might help your inverted nipple protract long enough for her to get a meal, only to retract after she has released your nipple. Your baby draws your areola and nipple inward and upward against the roof of her mouth. The gentle massaging and sucking stimulation protracts your nipple. Your nipple might invert once stimulation has ceased.
The skin around your nipples is elastic, changing throughout your pregnancy and especially in the baby's third trimester. Adhesions bind the skin at the base of the nipple to the underlying tissue in a way that prevents the nipple from stretching at the same rate as the skin surrounding it. When the cells in your breast become more elastic, some of the cells in your nipple and areola remain attached, pulling your nipple inward.
Some nipples invert after breastfeeding due to buildup of scar tissue, which diminishes the elasticity of skin cells in your breast. Vigorous breastfeeding lifts up the adhesions rather than stretching and breaking them, causing cracks in the nipple tissue. These cracks eventually lead to scarring and nipple inversion, which might induce pain or discomfort for the mother during breastfeeding.
Doctors have three grades by which they measure nipple inversion. In a grade 1 inversion, the nipple is inverted most of the time but can "come out" after tactile stimulation or exposure to cold. Grade 1 inversions can appear normal for quite some time after stimulation. Milk ducts usually are not compromised with grade 1 inversions and mothers may successfully breastfeed babies. Mothers with grade 2 inversion find it more difficult to stimulate the nipples into coming out, with the nipple returning to its inverted state almost immediately. Breastfeeding might be possible but not guaranteed. Women with grade 3 inversion cannot breastfeed and milk ducts are constricted.