We're Not on Earth Anymore! What Happens to the Human Body in Space?

Hey, Junior Astronaut, we need to talk about what happens to the human body in space.

Because, as glorious and full of wonders as it might be, space is not a hospitable environment for humans. It challenges the human body and even changes it. Some changes are short-lived, while others can affect astronauts for life.

If you imagine yourself becoming an astronaut and taking the next leap for humankind, you need to be aware of what your body will be facing — mentally and physically.

This article will explore the threats and effects space-travel can have on humans and the magic behind being able to travel so far in the first place. Plus, we'll learn how space agencies thoroughly prepare to keep their astronauts safe and healthy.

So, ready for an out-of-this-world trip? It's going to be bumpy.

The risks the human body faces in space

No oxygen, microgravity, and lots of radiation — these are just a few of the threats that await humans in space. And, while it might sound terribly frightening, there's nothing that can't be handled by science. So, let's see what the human body needs to face in space.


Without Earth's protective magnetic field, the human body is left defenceless in the face of radiation. And space has plenty of radiation sources to go around. The biggest three are galactic cosmic rays, solar radiation, and particles trapped in Earth's magnetic field. Zoiks!

Radiation is long known to be a threat due to its possible short and long-term impacts on our cells and DNA. That's why space agencies are pushing the boundaries of what's possible and are designing spaceships and spacesuits that reduce radiation exposure. Scientists are also continuously working on introducing safety procedures to save astronauts from spending too much time directly exposed to radiation.


Having only experienced Earth's gravity field, you might not understand how monumental gravity changes can be for the human body. Any transition from one type of gravity to another is indeed a challenge. And the challenge becomes even bigger if astronauts are to venture from one gravity field to another and then another — imagine a trip from Earth to the International Space Station (ISS), and then to Mars.

On the ISS, astronauts experience zero-gravity, which comes with its own set of tough challenges. For instance, the direction of how fluids circulate in the body is completely thrown aback, leading to disorientation, lack of coordination, loss of balance and even space motion sickness (yep, that's a thing!).

If — let's say — these same astronauts were then headed a mission to Mars, they'd have to readjust to yet another gravity field. Considering that Mars has one-third of Earth's gravity, their bodies would once again have to suffer through some changes. Yeap, space-motion sickness again.

Unpredictable environments and closed spaces

In space, even microbes behave differently. They can change their characteristics and even jump more easily from one person to another, especially in the closed environment of a spaceship.

That means that human bodies in space are more likely to develop illnesses and allergies. Uh-oh! Add to this the fact that astronauts' immune systems are already weakened by various other stressors, and you've got yourself a rather serious issue. However, if space agencies manage to create safe, well-oxygenated and thoroughly-ventilated indoor space systems, the risks can be drastically reduced.


Roaming through space is definitely one of the most amazing things anyone could experience. But it can also be complicated. Just imagine that you would be spending months on end in the same narrow environment, away from your loved ones, and surrounded by people who are, basically, strangers. This isolation can really take a mental toll on anyone.

So how do astronauts handle confinement? Staying focused on their end goal surely helps, but it's certainly not enough to combat fatigue, stress, and anxiety. Then what can be done? First and foremost, space agencies need to ensure crew members are compatible as a team. Secondly, they should include various relaxation activities to balance the work schedule. Thirdly, we all know how empowering a pep-talk from our close ones can be. So, continuous contact with those back home is the secret ingredient of a safe and happy space travel.

Altered circadian rhythm

The circadian rhythm is the natural process that regulates our internal rhythm here on Earth, and follows the day-night cycle of 24-hours. It helps us carry out the most essential functions of day-to-day life.

But what happens in space? Well, needless to say, the human body in space is completely out of tune with the circadian rhythm. For example, on the ISS, astronauts experience sunrise and sunsets every 90 minutes. This alteration can give rise to serious trouble for astronauts who can experience confusion, higher stress levels, fatigue, and even anxiety.

To keep things in check, several working protocols are set in place, to ensure that astronauts still maintain a 24-hour life rhythm.

The effects of space on the human body

The human body in space faces many threats. And, depending on how much time they spend in space, astronauts can feel the effects in various degrees. However, they have lots of aces up their spacesuits (and in their spaceships) to fight off the unwanted after-math of space-flight. Here's what they are faced with.

Muscles get weaker

Microgravity and different gravity fields change the way our muscles perform and react. Since the human body in space is exposed to lesser pressure than on Earth, our muscles tend to lose strength.

To maintain their tonus, astronauts need to work out intensely. However, even if they keep a strict 2 hours a day workout schedule, astronauts are still at risk of losing between 8 and 17% of muscle strength.

Microgravity affects the heart

On Earth, the veins in our body have to work against gravity to pump blood to our hearts. In space, however, fluids — unbound by gravity — circulate differently.

In the short-term, these changes can cause dizziness and headaches. In the long-term, they can affect the shape of the heart and even blood pressure. That is because more blood stays in the legs and is not redistributed to the heart.

Bone density is lost

On Earth, gravity and weight play an essential role in maintaining our bone density. In space, well, you know the drill. The lack of gravity changes the amount of pressure our bodies face. And facing lower pressure, our bones tend to lose density.

Fitness levels go down

Because of changes in their muscles, bones, and heart functions, astronauts are not as physically capable in space as they were on Earth.

To calculate the difference, scientists consider the maximum amount of oxygen that the body can use during exercise (measured through VO2 max tests). According to this, it appears the fitness levels of astronauts decrease by 20% to 25%, but tend to go back to normal after the first few months in space.

The immune system is challenged

Our immune system is our defence against disease. But to help it function at proper levels, our bodies need to be in tip-top shape. As you've already figured out by now, space can stress the human body. The alien environment leads to changes that also alter the immune system. Stress, radiation, microgravity, isolation and a complete shift in the 24-hours rhythm our body is used to, can prove to be very challenging for astronauts' immune systems.

To make up for this, astronauts can take flu shots before departure, and give their immunity a well-needed boost. Plus, they also spend some time in quarantine before their departure, to make sure they don't fall sick right before leaving for space.

How space agencies and astronauts prepare

There's no doubt that space is a dangerous place. But it's also a great environment that holds the answer to so many vital questions about life and our species. So exploring it is our duty.

And space agencies are doing their best to make sure their astronauts are safe and happy when leaving on a space mission. They conduct countless studies to understand exactly how the human body reacts in space, and bring continuous improvements to spacecraft' designs and spacesuits' functions.

As a future astronaut, you should be aware that you'll be facing difficulties. You'll need to study hard, and train even harder. To meet all the challenges that space imposes on human bodies, you'll have to undergo physical fitness programs and psychological adaptation training. Plus, you'll need to follow safety, nutritional, and health protocols to a tee.

Curious to discover how your body will behave in space?

Have a headstart and find out how your body would handle microgravity. We've prepared a zero-gravity programme that will sweep you off your feet — literally. Check out the details and have a taste of life in space.