Breast disease caused by the injection of permanent synthetic substances refers to injuries resulting from injecting synthetic materials into the breasts, usually for cosmetic reasons. The local or systemic inflammatory response after injection with a permanent filler depends on factors such as the injector, the individual’s genetic susceptibility, and the quantity and chemical makeup of the substance. Examples include silicones, paraffins, polyacrylamides, and various oils. Our literature review and personal experience suggest that complications can occur immediately or develop over time. Some cases from our research period from 1999 to 2024 are described in detail in this chapter. We want to highlight that injection-induced breast diseases may hinder early detection of breast cancer. This chapter also introduces a sixth-grade classification system for breast disease due to the injection of permanent synthetic substances, based on the complexity of symptoms.