So rare you may wonder if it is 'out of this world'... via Curiosity: There are eight common blood types. Keyword there? Common. If what you know about blood stops right around there, then this is all going to escalate very quickly. There are literally millions of varieties of blood types, and the rarest one is shared by fewer than 45 people on Earth. Talk about exclusive. Easy As A, B, O The ins and outs of blood types is way more complicated than you probably want it to be (or maybe that's just us?), but here's a relatively quick crash course. We are filled with red blood cells that carry oxygen through our bodies. Antigens cover these cells like sprinkles on a donut. The semblance of antigens on your red blood cells are like little name-tags that tell your body, "Hi, I go here," to which your antibodies respond, "Nice! The rest of us won't attack you." Your white blood cells latch onto these antigens to act as a shield against infection. The two main antigens are A and B. The kind