According to relevant research, there are many factors that will reduce human immunity under normal circumstances. For example: lack of sleep, irregular life, poor diet and so on. Then astronauts have basically collected these factors. Because they live in a narrow space for a long time, and day and night are upside down, their work is irregular and they don't have enough sleep, so they are affected to some extent in the weightless environment of space.

According to the data, when astronauts are in space, their immune function will become very disordered. Therefore, in severe cases, it will also lead to the decline of the function of some immune cells, and it is also impossible to respond relatively correctly to external attacks and threats in time. After astronauts return to earth, their immune function can't be recovered quickly, so they will be more susceptible to bacterial infection than ordinary people.

2. Muscle degeneration

When astronauts are in weightlessness, their skeletal muscles will not keep stretching as they did on earth, but will automatically contract. Also, when an astronaut stands, the muscles of his back and legs are not anti-gravity, so these muscles will gradually weaken and become smaller. On the worst 10 day, astronauts will lose 20% of their muscles in space.

In fact, the space company has already prepared corresponding training equipment for astronauts. Moreover, regular exercise and good diet can also prevent muscle degeneration. Therefore, the space station also has a lot of fitness equipment for astronauts to train in space every day, mainly to exercise chest muscles, triceps and so on.

However, although there are fitness equipment on the space station, it is difficult for these equipment to change the muscle degeneration that astronauts need to maintain a stable posture for a long time in a small range. For example, their skeletal muscles can only thicken after long-term exercise and stretching, so short-term training can't stop their muscle degeneration.

3. vision loss

The reason why every astronaut's vision should be checked before flying in the sky is because many studies show that space flight is likely to affect the astronauts' vision. For example: posterior compression of eyeball, retinopathy, sharp decline of vision and so on. The study found that 60% of astronauts flying in the sky will have vision loss.

At present, there are no specific practical factors to prove what causes the astronauts' eyesight to decline. But the weightlessness of the space station may be one of the chief culprits for this reason. Because in microgravity, human body fluids will be transferred. Such as intracranial pressure and intraocular pressure. Of course, there are other reasons for the data. For example, the proportion of carbon dioxide in the air in the space station is too high, and astronauts exercise and eat intensively inside, so this is also one of the reasons for the astronauts' vision decline.

4. Loss of body bones

Astronauts need to work on the space station for up to six months. Therefore, working in space for a long time, they are likely to have symptoms of osteoporosis due to bone loss. Therefore, for our human bone growth, we need to be stimulated by external forces to make the bone tissue in the body grow, thus reducing the risk of fracture. However, in the weightless environment in space, the stress on human bones will be greatly reduced, that is to say, there is almost no need to exert force on the body, and the bones will naturally not be squeezed, so they will not grow again, and the bones will lose their corresponding tissues.

Therefore, for astronauts, they lose almost 1.5% of bone tissue every month, but the pelvis and lower spine are the two parts of the human body with the most bone loss. In contrast, it takes one year for the elderly on earth to lose 1.5% of their bones. For the loss of human bones, even after astronauts return to earth, they can't return to their pre-flight state.

5. Exposure to high-intensity radiation

The reason why human beings are basically not affected by any space radiation on earth, but for astronauts living in space stations for a long time, they will be affected by solar radiation and other high-energy cosmic radiation in outer space. These so-called radiations are extremely harmful to human body. Even if the human body is not directly irradiated, when they collide with the aluminum shell of the space station, they will enter the living area of the space station and release a large number of secondary particles to the astronauts, thus causing so-called secondary damage to the astronauts.

So astronauts working in the space station are exposed to space radiation every day. Generally speaking, for astronauts, the amount of radiation received every day is about 1 millisievert, which is equivalent to receiving 8 X-ray chest films every day on the earth. So astronauts work in the sky for six months and receive the radiation equivalent to 60 years on earth. So this means that astronauts will suffer from high-intensity radiation and have a greater chance of getting cancer after returning to Earth.