Among the tasks of the ascent spacesuits is to ensure an acceptable external pressure for the astronaut, but even without a space suit, the tissues are strong enough to survive the excess pressure in the body. However, that doesn’t mean that taking off your helmet during a spacewalk is a good idea.
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The loss of ambient pressure changes the parameters of the blood stream – in particular, the boiling point of water decreases. Gas bubbles develop in the blood and the so-called caisson disease appears, also known to divers, for whom it can be fatal in case of rapid surfacing. Body gases escape through the skin, the lungs deflate quite naturally. The body becomes rapidly hypothermic, the water vapors desublimate into hoar frost, which mainly covers the mouth of the respiratory tract. Exposure to full sunlight will burn the skin, and after about ten seconds in the vacuum, the person will lose consciousness and suffocate within minutes. So taking off your helmet is definitely not recommended in free space…
