Why Nipple Inversion
If you have always had an inverted nipple then it is usually caused by shotened milk ducts and internal fibrous tissue.
If it is a new finding then see your doctor as it may represent a malignancy.
To correc this, i recommend trying a non surgical approach called the nipplette. It is a suction device that works for most women. It can be found on line and you do not need a prescription.