What could be the cause of inverted nipples?

Various: Inverted nipples occur due to variety of causes. These can be broadly classified as congenital (present since birth) or acquired (that develops later during the lifetime). Acquired conditions are:   breast abscess, breast cancer, recurrent infections, or prior breast surgery. Most are without complication, and even with invert. Nipples there are techniques to help breastfeed.

Multiple causes: Some women have naturally inverted nipples. If the nipples are normally everted and become inverted, there is more concern. One common cause is repeated episodes of infection/inflammation (periductal mastitis) which over time causes scarring and nipple inversion. Breast cancers also can result in nipple inversion/retraction. Therefore it is important to have an evaluation by a breast specialist.