How many red blood cells are circulating in your body right now?
Red blood cells are the single most common cell type in the human body, built almost entirely to ferry oxygen from your lungs to every other cell, and they're tiny and constantly being replaced.
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About 20-30 trillion. Red blood cells alone make up roughly 70-84% of all the cells in an adult human body by number, even though they're only a small fraction of its total mass.