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Reading this question about 1 mm tall people made me wonder: would a 1 mm tall person even be able to breathe? To someone of this size, the oxygen molecules around them would be much larger in proportion to their body, lungs and most importantly, cells. It seems like they might have difficulty with breathing enough oxygen in through their smaller lungs, and with their smaller cells bring able to process this oxygen.

  • Could a 1 mm tall person effectively process oxygen and continue to respirate, or would they asphixiate very quickly?

  • What would be the smallest a person could be and still successfully process enough oxygen to survive?

Note: I am aware that the 1 mm people in the question I referenced were actually robots. I'm specifically asking about a person that is 100% normal human, apart from being tiny.

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  1. A 1mm human or other mammal could not breathe. At that scale they would require an insect style tracheal system to move oxygen around their body.

  2. We know humans can breathe even at a size which prevents them being functional in other ways. Premature babies can breathe unassisted below 200mm in height (including legs which are non-essential), but can't survive for other reasons - for example they are not able to move unassisted due to the size of their head. A functional human smaller than this would require a different body plan, with the brain making up a smaller %age of their mass, and a relatively larger, faster beating heart. With adaptions like that, humans could exist as small as any other mammal (as small as 40mm) but not down to 1mm scale.

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    $\begingroup$ as an aside, birds can function with even smaller lungs than mammals, but this is because they have air sacs which increases their gas exchange efficiency $\endgroup$
    – Colin Pickard
    Commented Apr 27, 2016 at 12:27
  • $\begingroup$ Reptiles, amphibians and fish can get even smaller. If you're willing to step away from a mammalian origin, there are other vertebrates that can function very well at smaller scales. (1mm is probably pushing it for vertebrates though. The smallest currently known is an <8mm frog.) $\endgroup$
    – Darrel Hoffman
    Commented Apr 28, 2016 at 14:17
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No, they couldn't breathe with just scaled down human lungs. At that scale the surface tension of water would block all the brachi and Van der Waals would prevent the expansion of lungs in the rib cage.

At 1mm height a scaled down human would stick to every surface and would be unable to move at all. The increase in surface area to volume would cause them to freeze to death.

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