How do red blood cells squeeze through capillaries narrower than themselves?

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Blood plasma — blood Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).

Red blood cells are able to navigate through capillaries that are narrower than the cells themselves due to their unique structural adaptations. Mature human red blood cells are small, round, and biconcave, and they possess highly flexible membranes that allow them to deform as they pass through these tiny vessels.1

As they move through these extremely small spaces, the cells are capable of assuming a bell shape to accommodate the restricted diameter of the capillaries. This flexibility is essential for efficient circulation, ensuring that these cells can deliver oxygen to tissues throughout the body.1