What is Outer Space Like?
Outer space is the closest we can get in nature to a perfect vacuum. In a vacuum there is essentially no friction, allowing all bodies to move freely along their trajectories. This is an ideal situation, though; even in intergalactic outer space there are still a few hydrogen atoms per cubic centimeter. The deep vacuum provided by outer space does provide an attractive environment for many of Earth’s industrial processes, though, such as those that require extreme cleanliness.
Humans who are exposed to outer space will lose consciousness after just a few seconds and die within a few minutes due to hypoxia, which is a lack of oxygen in the blood. When the pressure of blood and other body fluids falls below 6.3 kPa (the vapor pressure of water at body temperature) they will boil. This is called ebullism. The steam will bloat the body and cause it to swell, but contrary to popular thought, a person will not explode when exposed to outer space. The tissues in the body are elastic and porous enough to prevent this from happening (Harding). Water vapor would evaporate from exposed areas in this environment, causing frost to form on such areas as the lungs, eyes, and mouth.
More dangerous than the vacuum environment is the rapid decompression that occurs with exposure to space. Eardrums, sinuses and even the alveoli in the lungs can rupture, causing blood loss, shock, and finally hypoxia. Even small drops in pressure can be fatal, if they occur too quickly.