What Happens To The Human Body In A Vacuum?

A NASA artist concept of future crews living and working on the Moon. NASA/Davidson

As humans get closer to living and working in space on a regular basis, a lot of questions arise about what it will be like for those who make their careers "out there". There is a LOT of data about what it's like from those who have lived and worked in space. In particular, the long-term inhabitants of people aboard the International Space Station, can tell us a lot about what it's like and what it does to their bodies.

Mission planners need that information as they plan missions to the Moon, Mars, and an asteroid. However, there's also have a lot of non-valuable "data" from Hollywood movies, where drama usually trumps scientific accuracy. They're there to tell a great story, and the real action of what happens in a vacuum isn't as exciting as directors might like. 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.

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.

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.  But, it will be a quick way to die if your spacesuit is damaged or you aren't rescued in time.


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. You wouldn't want to hold your breath. That would cause lung damage. You would probably remain conscious for several seconds, until the blood without oxygen reaches your brain.

It would be pretty darn cold, but the human body doesn't lose heat that fast, so you'd have a little time before you froze to death. It's possible you could have some problems with your eardrums, including a rupture, but maybe not. It would be worse if you had a cold, and were stuffy headed, with no way for the pressure to equalize.

You could get a bad sunburn, and you might actually swell some, but not to Arnold Schwarzenegger, Total Recall proportions. The "bends" are also possible, just like what happens to a diver who surfaces too quickly from a deep underwater dive.

While your own normal blood pressure will keep your blood from boiling, the saliva in your mouth could very well begin to do so. In 1965, while performing tests at the Johnson Space Center, a subject was accidentally exposed to a near vacuum (less than 1 psi) when his space suit leaked while in a vacuum chamber.

He did not pass out for about 14 seconds, by which time unoxygenated blood had reached his brain. Technicians began to repressurize the chamber within 15 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.

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, you would survive with few if any irreversible injuries.

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. 

Edited and updated by Carolyn Collins Petersen.