A transfusion reaction occurs when a patient's immune system reacts negatively to blood that has been transfused. This can happen if the blood type of the donor does not match the recipient's, leading to the body attacking the foreign blood cells. Symptoms may include fever, chills, rash, or even more severe complications. To prevent transfusion reactions, healthcare providers carefully match the blood types of both the donor and recipient. They also monitor patients closely during and after the transfusion. Understanding the importance of proper blood matching helps ensure safe and effective use of blood products in medical treatments.