The causes of nipple invagination include the following two main causes, as follows: 1. congenital nipple invagination: it is caused by congenital development, shortening of the breast ducts, partial tissue fibrosis contracture, and poorly developed nipple smooth muscle; 2. acquired nipple invagination: it is mostly caused by the nipple being pulled by pathological tissue in the breast, mostly due to inflammation, tumors, and other diseases that invade the ducts, ligaments, and fascia of the breast. The nipples are usually affected by inflammation, tumors and other diseases that invade the ducts, ligaments and fascia of the breast.