Nipple inversion, also known as a retracted nipple, describes a common anatomical variation where the nipple is pulled inward toward the breast tissue instead of protruding outward. This condition affects an estimated 10 to 20 percent of the general population, male and female, and is overwhelmingly a benign finding.
While most cases are present from birth or puberty, a newly acquired inversion can be a source of anxiety due to its association with underlying pathology.
The risk that an inverted nipple represents cancer is low, but any recent change necessitates a medical evaluation to rule out serious causes.
Understanding Nipple Inversion Grades
Nipple inversion is clinically categorized into three grades based on the degree of retraction and the ability to manipulate the nipple outward. This grading system provides a standard way for healthcare providers to assess the condition and potential for issues like breastfeeding difficulties. Congenital inversion, which has been present since breast development, is generally considered a normal variant of anatomy.
Grade 1 inversion is the mildest form, where the nipple can be easily pulled out with gentle pressure and maintains its outward projection. The lactiferous ducts are usually unaffected, and breastfeeding is generally possible. Grade 2 is characterized by a moderate degree of fibrosis, meaning the nipple can be manually pulled out but quickly retracts back inward upon release.
In Grade 3 inversion, the most severe classification, the nipple is fixed and cannot be pulled out at all, indicating significant fibrosis and shortening of the underlying milk ducts. While congenital cases across all grades are typically benign, the degree of inversion helps determine treatment options, such as non-surgical techniques for Grade 1 and surgical correction for fixed Grade 3 cases.
Statistical Risk of Malignancy
The risk that an inverted nipple is caused by malignancy depends heavily on whether the condition is congenital or newly acquired. Nipple inversion that has been present since puberty carries almost no risk of cancer. The concern arises specifically when a previously everted nipple suddenly begins to retract, particularly if the change is unilateral, affecting only one breast.
Studies suggest that 5 to 50 percent of newly acquired nipple inversion cases may be associated with malignancy. While this broad range highlights acquired inversion as a potential warning sign, the percentage is significantly lower when the inversion occurs without other clinical findings, such as a palpable lump.
In cases where breast cancer is the cause, the tumor cells infiltrate the milk ducts behind the nipple, causing scar tissue and fibrosis that physically pull the nipple inward. Therefore, the most concerning scenario is a new, one-sided inversion that is fixed and non-reducible, as this suggests a pathological process is actively tethering the nipple to the underlying tissue.
Common Causes of Newly Acquired Inversion
A previously normal nipple can retract due to several common, non-cancerous conditions. One frequent benign cause is mammary duct ectasia, involving the widening and thickening of the milk ducts, often affecting women in their late 40s and 50s. This condition creates inflammation and scarring that pulls the nipple inward, sometimes accompanied by a thick, sticky discharge.
Infections like mastitis or a subareolar abscess can also lead to acquired nipple inversion. The resulting inflammation and scar tissue formation can retract the nipple. Periductal mastitis, a chronic infection, is a recognized cause of nipple retraction, especially in individuals who smoke.
Other causes include trauma, such as a breast injury or prior breast surgery, where resulting scar tissue physically shortens the ducts. Fat necrosis, the formation of a lump from damaged breast fat, can also cause localized tethering and retraction. Natural age-related changes, where milk ducts shorten over time, can also cause the nipple to appear flat or inverted.
Critical Warning Signs Requiring Medical Evaluation
Any individual who notices a change in nipple shape, particularly a new inversion, should seek prompt medical evaluation. The most urgent warning sign is the sudden onset of unilateral nipple inversion, meaning the change occurs only on one side and was not present previously. Pathological inversion is typically fixed and rigid, meaning the nipple cannot be pulled out or everted, which suggests it is tethered by a mass or scar tissue.
The presence of a palpable lump or thickening in the breast or armpit alongside the inversion is a significant indicator that requires immediate investigation. Other associated warning signs include:
- Palpable lump or thickening in the breast or armpit.
- Dimpling of the breast skin that resembles the texture of an orange peel (Peau d’orange).
- Redness, scaling, or a rash on the nipple or areola that suggests Paget’s disease.
- Any spontaneous nipple discharge, especially if it is bloody or clear.