You would not explode in space, but you would certainly swell
Hollywood depicts space exposure as a sudden, violent explosion. The reality is far more unsettling. While you wouldn't burst like a movie character, the lack of atmospheric pressure triggers a biological process that turns your own bodily fluids into a lethal, expanding foam.
Contrary to cinematic tropes like 'Total Recall,' a human body exposed to a vacuum does not explode. Instead, the primary danger is the lack of pressure, which prevents liquids from remaining in a stable state. Without enough pressure, moisture on the tongue can begin to boil almost immediately. This process causes fluids to lose heat energy before they eventually freeze and evaporate entirely.
The physiological phenomenon known as ebullism describes how gases expand within the body. As internal gases and bubbles from boiling fluids expand, the body begins to swell significantly, much like a parade balloon. This expansion is not merely cosmetic; these bubbles can enter the bloodstream, potentially blocking circulation. Simultaneously, the lack of oxygen causes the brain to lose blood flow, leading to unconsciousness in approximately 15 seconds.
The physical damage extends to the vascular and respiratory systems. Blood vessels in the skin may burst, and internal organs can swell to the point of tearing. Attempting to hold one's breath is equally fatal, as the expanding gases would rupture the lungs. While the timeframe for survival is incredibly short—likely less than a minute—the biological mechanism is a slow, painful stretching rather than a sudden disintegration.
Beyond the vacuum itself, the space environment presents further thermal and radiological hazards. Depending on the location, an unprotected body might face thermal radiation of roughly 120 degrees Celsius or the loss of heat in the shade at approximately -100 degrees Celsius. For long-duration missions, such as NASA's planned trips to Mars, researchers are also focused on the 'RIDGE' hazards, specifically the difficulty of shielding against galactic cosmic rays.
Source: What Would Space Do To The Human Body?
