Which blood type is considered the universal donor?

Type O blood is considered the universal donor because it lacks A and B antigens on the surface of its red blood cells. This means that when Type O blood is transfused into recipients of different blood types, there is a significantly lower risk of an immune response from the recipient's immune system. Since Type A blood contains A antigens and Type B blood contains B antigens, the presence of these antigens can cause adverse reactions in people who have antibodies against them. Type AB blood, while able to receive blood from any type, contains both A and B antigens, making it unsuitable as a donor for individuals with other blood types. Thus, Type O blood's compatibility with all blood types allows it to safely donate to anyone in need of a blood transfusion.