What Happens to the Human Body in a Vacuum?

Nasa artwork of a crew of astronauts on the moon with a rover

NASA / Dennis Davidson / Wikimedia Commons / Public Domain

As humans get closer to the time when astronauts and explorers will be living and working in space for long periods of time, a lot of questions arise about what it will be like for those who make their careers "out there". There is a great deal of data based on long-duration flights by such astronauts as Mark Kelly and Peggy Whitman, but the life sciences experts at most space agencies need a lot more data to understand what will happen to future travelers. They already know that the long-term inhabitants aboard the International Space Station have experienced some major and puzzling changes to their bodies, some of which last long after they are back on Earth. Mission planners are using their experiences to help plan missions to the Moon, Mars, and beyond.

Crew members on the International Space Station work with a 3D printer inside the Microgravity Science Glovebox

However, despite this priceless data from actual experiences, people also get a lot of non-valuable "data" from Hollywood movies about what it's like to live in space. In those cases, drama usually trumps scientific accuracy. In particular, the movies are big on gore, especially when it comes to depicting the experience of being exposed to vacuum. Unfortunately, those movies and TV shows (and video games) give the wrong impression about what it's like to be in space. 

Vacuum in the Movies

In the 1981 movie "Outland," starring Sean Connery, there is a scene where a construction worker in space gets a hole in his suit. As the air leaks out, the internal pressure drops and his body is exposed to a vacuum, we watch in horror through his faceplate as he swells up and explodes. Could that really happen, or was that dramatic license?

A somewhat similar scene occurs in the 1990 Arnold Schwarzenegger movie, "Total Recall." In that movie, Schwarzenegger leaves the pressure of the habitat of a Mars colony and begins to blow up like a balloon in the much lower pressure of the Mars atmosphere, not quite a vacuum. He is saved by the creation of an entirely new atmosphere by an ancient alien machine. Again, could that happen, or was dramatic license at play?

Those scenes bring up an entirely understandable question: What happens to the human body in a vacuum? The answer is simple: it won't blow up. The blood won't boil, either. However, it will be a quick way to die if an astronaut's spacesuit is damaged. 

What Really Happens in a Vacuum

There are a number of things about being in space, in a vacuum, that can cause harm to the human body. The unfortunate space traveler wouldn't be able to hold their breath for long (if at all), because it would cause lung damage. The person would probably remain conscious for several seconds until the blood without oxygen reaches the brain. Then, all bets are off. 

The vacuum of space is also pretty darn cold, but the human body doesn't lose heat that fast, so a hapless astronaut would have a little time before freezing to death. It's possible that they would have some problems with their eardrums, including a rupture, but maybe not. 

Being marooned in space exposes the astronaut to high radiation and the chances for a really bad sunburn. Their body might actually swell some, but not to the proportions so dramatically shown in "Total Recall." The bends are also possible, just like what happens to a diver who surfaces too quickly from a deep underwater dive. That condition is also known as "decompression sickness" and happens when dissolved gases in the bloodstream create bubbles as the person decompresses. The condition can be fatal and is taken seriously by divers, high-altitude pilots, and astronauts. 

Astronauts train extensively underwater on Earth, wearing pressure suits, to simulate working in space
NASA / Bill Stafford / Wikimedia Commons / Public Domain

While normal blood pressure will keep a person's blood from boiling, the saliva in their mouth could very well begin to do so. There's actually evidence for that happening from an astronaut who experienced it. In 1965, while performing tests at the Johnson Space Center, a subject was accidentally exposed to a near vacuum (less than one psi) when his space suit leaked while in a vacuum chamber. He did not pass out for about fourteen seconds, by which time unoxygenated blood had reached his brain. Technicians began to repressurize the chamber within fifteen seconds and he regained consciousness at around the equivalent of 15,000 feet of altitude. He later said that his last conscious memory was of the water on his tongue beginning to boil. So, there's at least one data point about what it's like to be in a vacuum. It won't be pleasant, but it won't be like the movies, either.

There have actually been cases of parts of astronauts bodies being exposed to vacuum when suits were damaged. They survived due to quick action and safety protocols. The good news from all those experiences is that the human body is amazingly resilient. The worst problem would be lack of oxygen, not lack of pressure in the vacuum. If returned to a normal atmosphere fairly quickly, a person would survive with few if any irreversible injuries after an accidental exposure to vacuum.

More recently, astronauts on the International Space Station found an air leak from a hole made by a technician on the ground in Russia. They were in no danger of losing their air right away, but they had to go to some effort to get it plugged safely and permanently.

Edited and updated by Carolyn Collins Petersen.

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Greene, Nick. "What Happens to the Human Body in a Vacuum?" ThoughtCo, Aug. 28, 2020, thoughtco.com/human-body-in-a-space-vacuum-3071106. Greene, Nick. (2020, August 28). What Happens to the Human Body in a Vacuum? Retrieved from https://www.thoughtco.com/human-body-in-a-space-vacuum-3071106 Greene, Nick. "What Happens to the Human Body in a Vacuum?" ThoughtCo. https://www.thoughtco.com/human-body-in-a-space-vacuum-3071106 (accessed March 5, 2021).