A human body functions depends on Earth's gravity, hence the weightlessness of space can have noticeable affects on it, which can take years to recover.
In 2016 astronaut Scott Kelly returned home more nearsighted, lighter and with new symptoms of heart disease after spending a year on the International Space Station (ISS).
Scott's DNA even had some changes in comparison to his twin Mark Kelly, as nearly 1,000 of Scott's genes and chromosomes worked differently.
During his spaceflight, he aged around 9 milliseconds less because of ISS high rotation speed around the earth.
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NASA astronauts Sunita Williams and Barry Wilmore, who returned to earth on March 18, 2025 after an unplanned nine month stay, which started in June 5, 2024, are now being examined thoroughly for any immediate danger.
The two were stranded on the ISS after their Boeing spaceship malfunction and they had to wait for a ride home.
Here are some major changes that human body goes through in long space flights.
Face swelling
In micro-gravity, all the bodily fluids rush to the upper body and remain there, causing swelling in head and face, which eventually make legs shrink in size and loss mass.
Heart lose its shape
Total blood volume in space drops and with less blood to pump, the heart weakens and loses its shape, becoming more rounded.
As heart does not have to work against the gravity, with little work to do, heart will begin to atrophy.
Immunity
Due to radiation, several immune cells get destroyed and immunity receives a hit, along with some DNA damage that potentially increases the risk of cancer.
Body density
In space, bones become weaker and brittle.Each month astronauts lose around 1.5 percent of their bone and muscles, which eventually accelerate ageing.
Furthermore, the balance between the cells breaking down old bone and the formation of new bone is heavily disturbed.
Sight
Parts of the eyeball can flatten in no gravity causing sharper distance vision and dimmer near vision, with fluids flooding the skull, it can negatively effect smell and hearing capabilities.
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Notably, aside from physical changes and negative affects, the close confinement of spacecraft can have massive toll on a person's mental health, leading to lasting psychological stress.
