Which blood type is recognized as the universal donor for transfusions?

Blood type O negative (O-) is the universal donor because it can be safely transfused to recipients with any blood type. This versatility exists because O- red blood cells lack the A, B, and Rh antigens that could trigger immune responses in recipients. During medical emergencies when there's no time to determine a patient's blood type, O- blood is the safest option for transfusion. Ironically, while O- donors can give blood to anyone, they themselves can only receive O- blood due to their own immune system's sensitivity to foreign antigens.