18 What Happens to Your Body in Space?

Space is a lazy place. Your body floats all the time, so you don’t have to walk. And anything you pick up floats along with you, so your muscles don’t get much of a workout. It sounds wonderful to be able to fly everywhere you want to go, but that lazy environment causes your body to change in many different ways that are not healthy. And if you stay in space for too long, you may not be able to walk when you return to Earth.

When astronauts first arrive in space, they sometimes don’t recognize themselves. The fluids inside their bodies that would normally be pulled down by gravity float up into their chests, necks, and faces. Astronauts find that their chests expand a bit and their legs become skinny—“bird legs,” as they say. It also produces an effect called “puffy face.” The face becomes rounder and puffy. The astronaut’s eyes start to look squinty because of the swelling.

On Earth, gravity is always pulling the blood in our bodies down toward our feet. If it weren’t for the pumping action of our hearts, we would all have really fat legs and big feet from all the blood flowing down there. We’d also be unconscious because our brains need blood to think. Thankfully, our heart is always working to pump blood upward, against gravity, so that it’s circulated throughout the body to reach all the other parts, including our heads.

In space, that force of gravity is not present, so the blood is no longer pulled down toward the feet. The heart keeps pumping blood up toward head, but it remains there because there’s no force to pull it back down. All that extra fluid in the head makes astronauts feel stuffy in the nose, like they have a cold. To counteract that effect, some astronauts take cold medicine while in space.

Another effect of the puffy face and chest is that the body thinks it has too much blood, so it starts to get rid of red blood cells. That’s not a good thing because we need all of our blood to carry oxygen and other good stuff around the body. Our bones are affected in space as well. Our bones grow stronger the more we use them, and we use them all the time on Earth. Just standing up puts weight on your bones, allowing them to build strength as they hold you up. The more you walk, run, play sports, carry heavy things, or work out, the stronger and thicker your bones will become. Unfortunately, in space, where the body is weightless, our skeletons feel almost no force at all. When bones are not used, they become thinner. That’s a problem for astronauts because they need those bones when they return to Earth. In fact, when astronauts return home, they have to take it easy at first so they don’t break their bones while they regenerate.

To help prevent muscle and bone loss, astronauts living on the International Space Station have to exercise for two hours every day. They strap themselves onto a stationary bicycle, use bungie cords to hold themselves down to run on a treadmill, or use a spring device that simulates lifting weights.

If you’ve ever wanted to be a little taller, though, space flight might be for you. Your spine is a long chain of bones separated by soft discs. These discs act as shock absorbers so that walking on Earth is not so rough. In space, there’s no downward force on your spine, so the spongy discs expand, pushing the bones of the spine apart. And what does that mean? It means you get taller by several centimeters. While that sounds great in theory, the expansion also pulls on nerves in the spine, which can cause uncomfortable back pain.

You don’t need to go to the space station to find your space height, though. Try standing against a wall and have your friend place a pencil flat across the top of your head to mark how tall you are. Then lie down on the floor and have your friend make a mark right under your heel and another at the top of your head. Measure the difference between the two marks on the floor and compare it to your height on the wall. The floor marks should be slightly farther apart because your spine expanded slightly when you lay down.

Another body part affected in space is the eye. Some space farers see more clearly in space, especially those who need glasses on Earth. For others, their eyesight gets worse. Our eyes work in a way similar to cameras. Our eyeballs are shaped like round balls and are filled with a clear liquid. A lens on the front lets light in and makes an image on a screen, called the retina, located on the backside of the eye. The retina sends that image up to the brain through a nerve that comes out of the back of the eyeball. This whole system works together so that we can see.

The eyeball is not always perfectly round, though. Some people’s eyes are a little less spherical, so the lens does not make a clear image on the retina and they see the world as a blur. Glasses or contact lenses in front of the eye can correct the issue by focusing the light in the right way.

In the weightlessness of space, eyeballs that aren’t perfectly spherical sometimes become more rounded. The lenses focus in the right spot, which means those happy astronauts can put their glasses away for a while. Others, especially those who stay up in space for half a year at a time, find their vision gets worse and stays that way after they return to Earth. Doctors have found that extra fluid gathers in the brain and puts pressure on the eyes in space. In some cases, the optic nerve—the power cable that comes out of the eye and sends the image signal to the brain—becomes squeezed and bent from the pressure, so the signal to the brain is not as good. So far, there’s no way of knowing who will experience better or worse vision in space.

If you are the type of person who feels queasy on a roller coaster, gets seasick on a boat, or doesn’t feel well while riding in the back seat of a car, you may not enjoy flying in space, at least for the first day or two.

Motion sickness happens when our brain gets confused about what is happening to the body. Typically, the brain uses a variety of mechanisms to tell whether we are standing, sitting, moving forward or backward, turning left or right, spinning, or falling. The main input is through the eyes, which can see the world moving when we move.

But the brain also uses sensors in our skin—located on the bottoms of our feet, our hands, and our butts—so that we can feel pressure coming from different directions. Our ears act as important sensors, too. Behind our eardrums are little tubes called semicircular canals that are filled with liquid. When we move our heads, these liquids slosh around to tell the brain that the head is moving. It’s those liquid movements in our ears that help us keep our balance when we walk.

On Earth, all of these sensory inputs usually agree with each other. What the eyes see, the body feels, and that gives us a pretty good idea of where we are going. In space, the eyes still work, but most of the other sensors shut down. The body is floating all the time, so there’s very little pressure on the skin. The fluids in the ears swirl around in all directions, telling the brain that the body is falling, which it actually is (recall that weightlessness is just falling all the way around the Earth without hitting it). As a result, our brains in space get mixed messages. The eyes are saying the body is not moving, while the body is saying it is but doesn’t know in which direction. Whenever the brain gets confused, we react by feeling dizzy. And the brain, wondering what’s wrong, assumes the problems are due to some bad food you ate. It makes you sick, emptying your stomach just to rule out that possibility. About half of the people who fly in space feel nauseated for their first day or two.

It doesn’t help that our digestive system is meant for Earth and counts on gravity to make it work. When we eat food or take a drink, we also swallow a bit of air. This accumulates in our stomach and forms bubbles, which rise to the top of the stomach and travel up our throats in the form of burps. Later, as our digestive system breaks down the food, bacteria that live in our gut produce other gases, such as methane, which accumulate in our lower bowel, form bubbles, and burst out of the other end.

In space, these bubbles still form, but because there’s no downward pull of gravity, the bubbles don’t rise to our mouths. Instead, they remain suspended in the stomach or the intestines, giving a feeling of “foaminess” in the stomach. Astronauts feel like they want to burp, but it doesn’t happen, and if they do manage to get something up, let’s just say it’s usually pretty wet.

Finally, there’s something we all have to do that no one likes to talk about, but I’m going to do it anyhow. How do you go to the bathroom in space?

A space toilet looks a lot like its counterpart on Earth, with a few important differences. Two bars swing out across your thighs to keep you from floating off the seat, which is soft so that it feels comfortable and conforms to your body. There are also foot restraints so you really feel like you are sitting—remember, people don’t sit in space, they just float all the time, even while eating meals. But going to the toilet is something we like to do while sitting, so the space toilet is designed to make it feel like home.

Inside the toilet is a fan that draws air in under the seat and out through the bottom to act as a flush instead of water. The air flow makes sure that whatever you deposit in the toilet goes in the right direction. If all you need to do is pee, there is a suction hose with a cup on the end that is custom made for each crew member.

When everything is done, you use hand wipes to clean up, then the toilet lid is closed and the waste material inside is exposed to the vacuum of space, which freeze-dries it and kills all the bacteria.

That covers just a few of the unusual things that happen to the human body in outer space. But the truth is, we’re still learning about the effects of zero gravity on our bodies, and as we learn more, we’ll no doubt make further discoveries that alter how we conduct space travel.

One thing we know for sure is that flying in space is wonderful, but it takes astronauts away from their families and away from nature. Life in space is life spent in a tin can. Even if you’re lucky enough to go on a space walk, you have to wear a bulky space suit, so you are not really outside or in nature. On very long journeys, astronauts begin to miss their family and friends, the smell of flowers, and the feeling of wind and rain on their faces. Fortunately, they now have access to the internet, so they can make regular calls to home.

If you’re a person who can stay strong by exercising every day, doesn’t get dizzy while moving in all directions, is willing to risk poor eyesight, doesn’t mind having a foamy stomach, and is okay being away from friends and family for long periods of time, you could be astronaut material!