You would still die, of course, but it would be from suffocation. The blood holds enough oxygen for about 15 seconds of brain activity. As astrophysicist Paul Sutter told Forbes, temperature is a measure of the amount of energy atoms and molecules have to move, and since space is almost empty, there isn't much to move, causing it to cool down. This also means that there is no matter in space to transfer heat to.
However, a person could freeze due to the evaporation of water from their body and the slow loss of heat through radiation emanating from their body. Sudden loss of pressure will also cause decompression sickness due to nitrogen bubbles in muscles and bones, as well as a lack of oxygen, known as “hypoxia”. In fact, it's the loss of oxygen that will kill them first. Depending on where you are in space, this will take between 12 and 26 hours, but if you're near a star, you'll burn to a crisp.
When the Earth blocks the Sun, the temperature around the space station is around -157 °C (-250 °F). You start to remember your training and what those NASA nerds explained would happen in the unlikely event that you ended up launched into space without a spacesuit. You decide to take advantage of this short time and immediately quickly press the holographic screen of your wristwatch to alert the rest of the space station crew. However, the space is practically empty, which means that anyone who is unfortunate enough to find themselves unprotected in such an environment will experience rapid internal decompression.
The only viable means of transferring heat between two objects, in this case the human body and the space we have left, is radiation. But because there is practically no atmospheric pressure in space, the boiling point of liquids decreases significantly. Space is a vacuum devoid of air, which means that, unlike Earth, there is no atmosphere or pressure exerted by air molecules. It's been a second since you stupidly launched yourself out of the space station, basically naked in space.
Lacking oxygen, the brain will go into “safe mode” to conserve energy about 15 seconds after being exposed to the vacuum of space. When the International Space Station looks at the Sun, the outside temperature is around 121 °C (250 °F). The film Mission to Mars has a scene that realistically demonstrates what would happen if an astronaut's spacesuit rapidly lost pressure and was exposed to outer space. Seconds later, you find yourself floating through space without a spacesuit, wearing only typical astronaut pajamas. In 1966, a NASA aerospace engineer, Jim LeBlanc, was helping test the performance of prototype spacesuits in a huge vacuum chamber. The effects of being exposed to outer space for five seconds are dire and potentially fatal.
Without protection from a spacesuit or other form of insulation from extreme temperatures and lack of oxygen, death would be almost instantaneous due to suffocation or hypoxia. The human body would also experience rapid decompression due to nitrogen bubbles forming in muscles and bones as well as rapid freezing due to evaporation and radiation loss. The only way for someone who finds themselves unprotected in outer space for five seconds or more is to take advantage of their limited time by alerting their crewmates as soon as possible. Unfortunately, even with quick action taken by those on board the spacecraft or station they are on, death is almost certain.
