What happens to the human body when it is directly exposed to space?

It is well known that space is dangerous for humans. Suppose you are an astronaut exploring the vastness of space and are accidentally thrown out of the airlock of the spacecraft. Suppose you are not wearing a spacesuit at this time, and thus directly exposed to the vacuum of space, then your body will have what changes?

In many Hollywood films there are these plots, but most of them are exaggerated descriptions of the situation. People inside the movie would immediately explode or be instantly frozen without the protection of a helmet or spacesuit. But in reality, although a similar situation can happen, it is obviously not as exaggerated.

In fact, if an astronaut floats in space without a space suit although they will not survive, their death occurs within minutes, not seconds. Unlike on Earth, there is no air in space, and there is no atmosphere or pressure generated by the molecules in the air. The difference in air pressure causes liquids to boil and vaporize at different temperatures. If the air pressure above a liquid is high, such as at sea level, then it is difficult for bubbles in the liquid to form and rise to the surface to evaporate. With almost no air pressure in space, the boiling point of a liquid will be relatively low. The human body is composed of 60% water, in the case of almost zero pressure, the water in the human body will quickly boil to gas. Then the human body tissues in this case will begin to expand.

Some people who have been exposed to near-vacuum conditions and survived tell how this happens. In 1966, Jim LeBlanc, a NASA aerospace engineer, tested the performance of a spacesuit in a vacuum chamber. During the test, the hose carrying pressurized air from the spacesuit was blocked. He recalls in a documentary, "Before I lost consciousness, I felt the saliva start to bubble on my tongue, and that's the last thing I remember."

For deep-water divers, a similar situation can happen when they surface quickly and switch quickly from a high-pressure environment underwater to a low-pressure state at the surface. And for astronauts who don't wear spacesuits, venous blood doesn't boil as fast as tissue fluid because there is some internal pressure in the body's circulatory system. Back in 2013, an article in Aerospace Medicine and Human Performance, which studied animals and humans exposed to a vacuum, showed that the subjects were rendered unconscious within 10 seconds. Then some of them began to lose control of their bladder and intestinal systems, and swelling of the muscles blocked the flow of blood to the heart and brain. Some scientists said that almost no one could survive this situation and would die within two minutes.

NASA's Biological Astronautics Data Book writes that the vacuum pulls air out of your lungs, thus causing a choking situation. It then continues to pull gas and water vapor out of the body through the airways. The boiling evaporation of water will quickly take heat away from the body, with the area around the nose and mouth being the first to freeze. The temperature of the rest of the body then decreases at a relatively slow rate because there is less water in these areas, so less water evaporates.

Astrophysicist Paul Sartre once told Forbes that temperature is a measure of the amount of energy used to move atoms and molecules. Yet there is almost nothing in space, let alone energy, so it is "cold". So a person could be frozen by the slow loss of heat as water evaporates from the body and radiates body temperature.

What exactly have we learned from these scientific studies and knowledge? That is to always wear a spacesuit.