It's easy to imagine Superman or some other superhero whizzing through space without a care in the world. Put a human in that same situation though, and this sweet fantasy turns into a blood curdling nightmare. In the vast nothingness of space, the unprotected human body is attacked at every atomic level. You burn, freeze and experience a complete cellular transformation, and yes, it's painful.
Here is what happens to the unprotected human body in space.
1. Boiling Blood
The lower the pressure, the lower the boiling point of any liquid in that environment. Since there's no pressure in space, an exposed body would have to go through the terrible (and slightly fascinating) experience of feeling their blood literally boil inside them.
2. Enlarged Veins
Due to the body contorting effects of space, your veins would be enlarged to almost ten times their regular size. Your heart would obviously not be able to pump enough through these red tunnels, and you'd have to bid goodbye to your body, mind, etc. Basically you'd die.
3. Loss of Bowel Control
In an environment of such great vacuum, it's easy to understand that your lungs would be drained of air. However, after your lungs, your bowels follow suit. You'd be floating in space with little bits of poop all around you.
4. Massive Swelling
While it has been clarified that you won't explode like in Total Recall, the boiling blood would make your skin bloat and puff up. Not in the fun roly-poly way either, but in a pain-is-my-only-friend kind of way.
5. DNA Change
After initially getting excited, it was finally clear that even though you experience cell mutation in space, it just means that you're very likely to get cancer later. This is because there's no protection from a solar system chalk full of UV rays, gamma radiation and other danger dots.
6. Exploding Lungs
One of the worst things is taking a deep breath of air before plunging into space. This is because the air would expand massively in your chest in the low pressure environment of space, and your lungs would explode like balloons
7. Nitrogen bubbles in Body
In the highly vacuum like environment of space (which is basically the reason for all this suffering), nitrogen bubbles pop up all over the inside of your body. This can cause joint pain, strokes and sudden death.
8. Superfast Freezing
Since there's no humidity in space, all the watery parts of your body would be liable to freeze since the temperature is so low. So your sweat, your eyes, mouth and finally your respiratory tract would freeze. Ice breath!
9. Extreme Burns
Any part of your skin that is exposed would be horribly sunburned in space. Without the ozone layer to protect your special places, you'd have the most pain ful tan in history. Also, you look straight at the sun from space and you will actually go blind.