What Happens To The Human Body In A Vacuum?

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, and explodes.

A somewhat similar scene is 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.

what happens to the human body in a vacuum?

No, the body won't blow up. Your blood won't boil, either. 

There are a number of things about being in space, in a vacuum, which could cause harm to the human body. You wouldn't want to hold your breath. This 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 a diver who surfaces too quickly.

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 NASA facility now known as 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.

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. The results were negligible.