One of the most effected organs in an astronaut’s body is the heart, which no longer has to work as hard to pump blood all over the body while in space.
In fact, during their time in space, astronauts can lose as much as 22% of their total blood volume, and there’s a high risk of heart atrophy as the organ slows down with less blood to pump. Exercise helps to keep the heart healthy and prevent its gradual wasting away, but astronauts are prone to dizziness and even fainting.
One of the biggest concerns about time spent in outer space is exposure to radiation, which can lead to both short- and long-term problems.
Spending a year in space opens up an astronaut to about 40 times the radiation that someone on Earth would experience in that same amount of time. This can affect bone marrow, the immune system, and especially the eyes.
Many astronauts report suffering from “cosmic ray visual phenomena,” in which they have trouble sleeping due to seeing bright flashes of cosmic rays across their eyeballs.
Some of the strangest occurrences have to do with the body’s distribution of liquids.
In their first few days in space, astronauts notice that their faces are often fatter and their legs are skinnier as the body readjusts to not having to deal with gravity.
The bottom of feet often get smoother as calluses fade away. On the other hand, the tops of feet can become extremely sensitive and even raw.