Inflammation serves as a defense mechanism against infection and injury, and localizing and eliminating injurious factors and removing damaged tissue components allows the healing process to begin. During the healing process, damaged cells capable of proliferation regenerate. Tissue repair, resulting in scar formation, may occur when normal tissue architecture cannot be regenerated successfully. Failure to replicate the original framework of an organ can lead to disease. Acute inflammation is usually beneficial but often causes unpleasant sensations, such as pain or itching. In some instances inflammation can cause harm. Tissue destruction can occur when the regulatory mechanisms of the inflammatory response are defective or the ability to clear damaged tissue and foreign substances is impaired. In other cases an inappropriate immune response may give rise to a prolonged and damaging inflammatory response. In autoimmune reactions, the body’s immune system attacks its own tissues, leading to long-term chronic inflammation.