If an astronaut is exposed to a space vacuum without protection, other nasty stuff would happen, too. Without atmospheric pressure to balance things out, the unfortunate space traveler's final breath would expand in his or her lungs, tearing the delicate gas-exchange tissues that line them. At the same time, water in the person's soft tissues would vaporize, causing the body to swell up grossly, though the skin would provide enough resistance to keep him or her from bursting like an overinflated balloon. Bubbles would form in the veins, blocking blood flow, and the astronaut's bowels, bladder and stomach would expel their contents. (This was what happened to dogs exposed to near vacuum as part of a study. If the time they spent was less than 90 seconds, most of the effects went away once the air was repressurized; more than that and they usually died) [source: Gosline].
If that's not bad enough, a condition called ebullism can set in, in which the boiling point of bodily fluids would decrease below the body's normal temperature, causing the astronaut's saliva to boil on his or her tongue [source: NASA].