For more than 50 years now, humankind has been venturing into space in order to learn more about the Earth and the rest of the universe surrounding us. We've been to the moon, set up a permanent space base in the form of the International Space Station, and are already planning a mission to Mars.

However, while our accomplishments have been undoubtedly amazing, the people who took part in the missions saw noticeable differences in their bodies - often negative - while in space and after returning back home. Based on decades of studies, here are 10 known side-effects of visiting outer space...

1. Balance difficulties

A person's balance is regulated using a mechanism in their inner ear. In space, however, this mechanism has to readjust to a difference in gravity. Because of this, astronauts can feel nauseous while adjusting to microgravity and may have to re-familiarize themselves with how to comfortably walk on solid ground when they return to Earth.

2. Loss of bone density

Because there isn't as much gravity in space, the body doesn't have to work as hard to keep us sitting/standing/moving around. This causes the bones to lose vital minerals (potentially leading to abnormally high levels of calcium in the blood and increased risk of kidney stones), which in turn causes bone density to decrease by more than one percent every month. To put that in context: elderly men and women lose around one to one-and-a-half percent per year.

3. Weakened muscles

As with the above point, because the body doesn't have to work as hard to counteract the forces of gravity, meaning that muscles get weaker. To prevent this from happening, astronauts have specially designed exercise equipment to help sustain muscle density.

4. Vision problems

In space, fluids cannot travel around the body as easily and end up accumulating in the head rather than circulating down to the legs. This "fluidic drift" can put pressure on the optic nerve, causing vision problems. This is something that NASA is trying to counteract before pursuing longer-duration missions.

5. Exposure to radiation

Astronauts are exposed to higher levels of radiation in space than on Earth, putting them at risk of long-term health conditions such as cancer, or even drastic changes to their DNA.

6. Dehydration

Because of a change in nutrition and the way that fluids move around in the body, it's much easier to become dehydrated in space than on Earth. Though this may not sound like a big deal, it can become a serious issue if left untreated.

7. Disturbed sleep

If a person isn't experiencing the same 24 hour days that they're used to on Earth, their circadian rhythm can fall out of sync, leading to sleep problems. What's more, a small and noisy living space coupled with a high-stress task can make it very difficult to sleep under any circumstance - let alone while floating through the cosmos.

8. Mental health problems

Being sent on a mission in space is no easy feat, and many astronauts end up suffering from depression and/or anxiety due to the intensity of their work. Surviving in space is much harder than it is on Earth, and astronauts have to go for months at a time without seeing friends or family.

9. Changes in gene expression

A study of twin astronauts - one of whom stayed on Earth while the other went into space - showed that leaving the Earth's atmosphere causes a change in a person's gene expression. Some of these changes reverted back to normal after being back on Earth for a while, while others could be permanent.

10. Age slower

Due to a principle of physics known as time dilation, astronauts who spend a significant amount of time in space have technically aged less than the rest of us down here on Earth. However, don't get too excited, as a six-month stint on the ISS will only save you 0.007 seconds of ageing.

So, while being an astronaut might seem like one of the coolest jobs in the world, it's also probably one of the riskiest. The people who dedicate their lives to exploring the universe have got to be pretty tough individuals, and it's crazy to think that they go on these missions even though we still don't fully understand how the human body can be changed by the experience.

For more than 50 years now, humankind has been venturing into space in order to learn more about the Earth and the rest of the universe surrounding us. We've been to the moon, set up a permanent space base in the form of the International Space Station, and are already planning a mission to Mars.

However, while our accomplishments have been undoubtedly amazing, the people who took part in the missions saw noticeable differences in their bodies - often negative - while in space and after returning back home. Based on decades of studies, here are 10 known side-effects of visiting outer space...

1. Balance difficulties

A person's balance is regulated using a mechanism in their inner ear. In space, however, this mechanism has to readjust to a difference in gravity. Because of this, astronauts can feel nauseous while adjusting to microgravity and may have to re-familiarize themselves with how to comfortably walk on solid ground when they return to Earth.

2. Loss of bone density

Because there isn't as much gravity in space, the body doesn't have to work as hard to keep us sitting/standing/moving around. This causes the bones to lose vital minerals (potentially leading to abnormally high levels of calcium in the blood and increased risk of kidney stones), which in turn causes bone density to decrease by more than one percent every month. To put that in context: elderly men and women lose around one to one-and-a-half percent per year.

3. Weakened muscles

As with the above point, because the body doesn't have to work as hard to counteract the forces of gravity, meaning that muscles get weaker. To prevent this from happening, astronauts have specially designed exercise equipment to help sustain muscle density.

4. Vision problems

In space, fluids cannot travel around the body as easily and end up accumulating in the head rather than circulating down to the legs. This "fluidic drift" can put pressure on the optic nerve, causing vision problems. This is something that NASA is trying to counteract before pursuing longer-duration missions.

5. Exposure to radiation

Astronauts are exposed to higher levels of radiation in space than on Earth, putting them at risk of long-term health conditions such as cancer, or even drastic changes to their DNA.

6. Dehydration

Because of a change in nutrition and the way that fluids move around in the body, it's much easier to become dehydrated in space than on Earth. Though this may not sound like a big deal, it can become a serious issue if left untreated.

7. Disturbed sleep

If a person isn't experiencing the same 24 hour days that they're used to on Earth, their circadian rhythm can fall out of sync, leading to sleep problems. What's more, a small and noisy living space coupled with a high-stress task can make it very difficult to sleep under any circumstance - let alone while floating through the cosmos.

8. Mental health problems

Being sent on a mission in space is no easy feat, and many astronauts end up suffering from depression and/or anxiety due to the intensity of their work. Surviving in space is much harder than it is on Earth, and astronauts have to go for months at a time without seeing friends or family.

9. Changes in gene expression

A study of twin astronauts - one of whom stayed on Earth while the other went into space - showed that leaving the Earth's atmosphere causes a change in a person's gene expression. Some of these changes reverted back to normal after being back on Earth for a while, while others could be permanent.

10. Age slower

Due to a principle of physics known as time dilation, astronauts who spend a significant amount of time in space have technically aged less than the rest of us down here on Earth. However, don't get too excited, as a six-month stint on the ISS will only save you 0.007 seconds of ageing.

So, while being an astronaut might seem like one of the coolest jobs in the world, it's also probably one of the riskiest. The people who dedicate their lives to exploring the universe have got to be pretty tough individuals, and it's crazy to think that they go on these missions even though we still don't fully understand how the human body can be changed by the experience.