There are 3 grades of Nipple Inversion
Grade 1 refers to nipples that can easily be pulled out, by using finger pressure around the areola. The Grade 1 inverted nipple maintains its projections and rarely retracts. Also, Grade 1 inverted nipples may occasionally pop up without manipulation or pressure. Milk ducts are usually not compromised and breast feeding is possible. These are “shy nipples”.
Grade 2 is the nipple which can be pulled out, though not as easily as the Grade 1 inverted nipple but which retracts after pressure is released. Breast feeding could be possible even though it is more likely to be either very difficult or impossible. Grade 2 nipples have a moderate degree of fibrosis. The lactiferous ducts are mildly retracted but do not need to be cut for the release of fibrosis.
Grade 3 describes a severely inverted and retracted nipple which can rarely be pulled out physically and which requires surgery in order to be protracted. Milk ducts are often constricted and breast feeding is impossible. People with Grade 3 inverted nipples may also struggle with infections, rashes, or problems with nipple hygiene.