The human body needs protection in low-pressure environments (e.g the vacuum of space or Mars’ low atmospheric pressure). Without protection, gasses in the body expand and liquids sublimate away, basically making the normal function of bodily systems impossible.
Gas partial pressures and operating pressures of suits and habitats are huge topics that I am not getting into here right now. What I want to mention is something that is a little surprising: skin itself is gas-tight and does not need as much protection as one would guess. All that is required is mechanical compression in order for it to maintain its normal shape and function.
The idea of mechanical counter-pressure (MCP) spacesuits originated in the ’60’s. But only recently have materials evolved to make such a suit practical. Maybe. Research is ongoing.
For future astronauts, the process of suiting up may go something like this: Instead of climbing into a conventional, bulky, gas-pressurized suit, an astronaut may don a lightweight, stretchy garment, lined with tiny, musclelike coils. She would then plug in to a spacecraft’s power supply, triggering the coils to contract and essentially shrink-wrap the garment…