Transfusion reactions are adverse responses that can occur when a patient receives a blood transfusion. These reactions happen when the immune system identifies the transfused blood as foreign, leading to symptoms like fever, chills, or rash. The most common cause is a mismatch between the donor's and recipient's blood types, which is why proper blood typing is crucial before any transfusion. There are different types of transfusion reactions, including hemolytic reactions, which can be severe and even life-threatening. Other reactions, like allergic reactions, may cause mild symptoms but still require monitoring. Healthcare providers are trained to recognize and manage these reactions to ensure patient safety.