Space travel is exciting, but it is also very hard on the human body. Our bodies are designed to live on Earth, where we have gravity, fresh air, and protection from harmful radiation. But in space, everything is different—there is no gravity, astronauts are exposed to strong radiation, and they have to live in small spaces for a long time. These conditions can cause many changes in the body, and some effects may last even after astronauts return to Earth.

Scientists are studying these changes to find ways to keep astronauts safe and healthy. However, there is still a lot we don’t know, especially about what might happen if humans live in space for many years or even for generations.

The danger of space radiation

One of the biggest dangers of space travel is exposure to space radiation. On Earth, we are protected by our atmosphere and magnetic field, which block most harmful radiation from space. But astronauts in space do not have this protection.

"Unlike on the Earth, where the atmosphere and planetary magnetic field provide a shield from space radiation, astronauts are exposed to high-energy radiation permeating the cosmos. This can lead to DNA damage, increased cancer risk, neurodegenerative effects, cardiovascular issues, and immune system dysregulation."

Astronauts who stay close to Earth, like on the International Space Station (ISS), get some protection from Earth’s magnetic field. But those who travel farther, like to the Moon or Mars, face much stronger radiation. This radiation can be very harmful and may cause serious health problems. Scientists are still trying to find the best ways to protect astronauts from these dangers.

How microgravity affects the body

On Earth, gravity plays a big role in how our bodies function. But in space, there is no gravity, and this causes major changes in the body.

"Without gravity, bodily fluids shift upward, leading to facial swelling and increased intracranial pressure, which can affect vision. The lack of mechanical loading on bones and muscles associated with the downward pull of gravity leads to bone density loss and muscle atrophy."

Astronauts' hearts and blood flow change in space, making it harder for their bodies to control blood pressure when they come back to Earth. They may also struggle with balance and movement because their inner ear, which helps with coordination, works differently without gravity.

Spending a long time in space can make these problems even worse. Scientists are trying to find ways to help, like special exercises and medicines, but there are still many challenges to solve.

Mental health challenges in space

Space travel is not just physically demanding—it is also mentally and emotionally challenging. Astronauts must live in small, enclosed spaces for long periods, far from family and friends. This can cause psychological stress.

"Long-duration space missions require astronauts to live in confined and isolated environments with limited social interaction and exposure to natural stimuli. This can lead to psychological stress, sleep disturbances, cognitive performance declines, and mood disorders."

Being in space for a long time can also lead to conflicts among crew members, which can affect mission performance. Scientists are studying ways to support astronauts' mental health, such as better communication with Earth and structured schedules to maintain a sense of normalcy.

What happens when astronauts return to Earth?

Coming back to Earth after space travel is not easy. The body needs time to get used to gravity again. How quickly an astronaut recovers depends on how long they were in space.

For short trips of just a few days, most of the damage the body experiences in space heals quickly—about 95% of it goes away after returning. But astronauts who spend months in space, like those on the International Space Station (ISS), take longer to recover. Some problems, like vision changes, may not fully go away.

One serious issue is spaceflight-associated neuro-ocular syndrome (SANS), which affects eyesight. It happens because microgravity causes fluids in the body to move differently, putting pressure on the eyes. Some astronauts have long-term vision problems and may need glasses.

Scientists are also studying mitochondria—tiny parts of cells that create energy—to understand how space affects the body and find ways to keep astronauts healthy.

What we still don't know

There are still many gaps in our understanding of how space travel affects the human body. For example, scientists do not fully understand how space travel impacts lung function, mental health, or brain plasticity (the brain's ability to change and adapt). While it is known that space radiation increases cancer risk and accelerates ageing, the exact biological processes behind these effects are still being studied.

"Scientists also lack a comprehensive understanding of how microgravity, radiation exposure, and isolation impact cognitive function, mental health, and neuroplasticity—the brain’s ability to change and adapt—over long durations."

One of the biggest unknowns is how space travel affects human reproduction. Very few studies have been done on this topic, and most involve animals like mice. If humans are going to live in space long-term, understanding how space affects fertility, pregnancy, and child development will be essential.

New research findings

Recent studies have helped scientists learn more about how space travel affects the body. A 2024 study found that space travel changes many parts of the body, including the brain, heart, muscles, kidneys, skin, and immune system. It also confirmed that mitochondria, which produce energy in cells, are affected. Another study in 2024 showed that astronauts get headaches more often than expected—out of 24 astronauts on the ISS, only two did not have headaches.

In 2023, researchers found that astronauts on long missions had changes in their brains, with fluid-filled spaces getting bigger. A 2022 study discovered that astronauts lost bone density while in space, and some did not fully recover even after a year back on Earth.

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