12 Scary Changes in Your Body after 5 Months Being in Space

Adam Shaari
8 min readAug 3, 2020


Five-months trip to ISS should not be in your honeymoon plan.

Human is designed to live in the Earth’s atmosphere, pulled by the Earth’s gravity. A trip to International Space Station is the dream of many but it might not be as pleasant as how we imagined. Simply by not living in the Earth’s atmosphere while being pulled by the Earth’s gravity, can give a temporary and permanent effects on your body.

  1. Losing up to 10% of your bone density.

On average, astronauts lose about 1% to 2% of their bone density each month. This adds up to around 10% after 5 months. This is due to the fact taht bones do not permanent calcium structures. Stress that is exerted upon affects the structure of the bones. If you do not put enough stress on your bones, it will become weaker, just like muscles. The absence of Earth’s stronger gravity spares the bones from supporting the body, thus leads the loss of bone density. In ISS, restraints are used to strap the astronauts to a treadmill in order to produce needed weight bearing environment. This does help to decrease the rate of bone loss, but does not eliminate the problem at all.

2. Losing 40% of muscle mass.

Certain groups of muscles are constantly used to support ourselves to stand against the gravitational pull. The weightless environment requires much less stress on the muscles. Moving around and supporting the body requires less muscle contraction. Lack of regular use and exercise weaken and even deteriorate the muscle. Astronauts can lose up to 40% of their muscle mass throughout the course of 5 months in ISS. In order to combat the effect of muscle loss, astronauts do strength training, adequate exercise followed by proper diet. They can regain the pre-flight muscle mass once they returned to Earth, however, it is crucial that they do not lose high percentage of muscle mass. They need all the mobility function to execute all the tasks planned, especially for long duration space missions.

3. Your heart grows weaker (even becomes more spherical!).

Pumping the blood to the whole body requires less work in microgravity environment as there is no gravity to pull you down. You also lose your heart muscle (cardiac muscle) due to the less work done by the heart. This leads to the cardiac problems and even the changes of the shape of the heart to be more spherical.The heart becoming more spherical is an indicator that the heart in functioning less efficiently. One study shows that the heart becomes 9.4% more spherical in space. However, the condition seems to be temporary as the heart returns to its more elongated shape after some period of time the astronauts return to Earth.

Astronaut Chris Hadfield live demonstration from ISS.
Aastronaut Chris Hadfield during Conan interview.

Notice that this is always how their face looks like when their are in space where there is no gravity? This is almost the same as the face of someone hanging upside down. On Earth, we have the Earth’s gravity to pull down the blood in the upper part of your body. In space, the blood stays in the head and chest more and longer that it should. Bulging blood vessel and puffy face may not be the main concern as the insufficiency of blood flow to and from the brain can them to feel dizzy and even faint upon adjusting to Earth’s gravity. One study shows that more than 80% of astronauts have experienced dizziness after returning from space.

4. Brain — Alzheimer’s disease development.

On Earth, the Earth’s magnetic field protects the planet from harmful radiation. In space the astronauts are subjected to continuous cosmic rays and space radiation particularly HZE particles. Long period space expedition is the one that is most affected by this. Manned missions to an asteroid in 2025 and Mars by 2035 forces scientists to work on combating the effect of space radiation. Neurodegeneration specifically the development of Alzheimer’s disease is one of the main concern of the exposure to space radiation. The mass and speed of HZE particles enables them to penetrate even solid objects like spacecraft and astronauts and coating the spacecraft with 2 meters of lead or concrete may not be the solution to this situation.

A series of experiments were done on mice dosed with radiation shows that a significantly high level of beta amyloid, a type of protein in the brain that is associated with Alzheimer’s disease. Brain cells that process, store and retrieve information degenerate and die due to Alzheimer’s disease. One of the identified cause of that is due to the interruption and disruption of communication between brain cells by beta-amyloid.

5. Eyes — Visual problems and cataracts.

Human eyes are designed for the condition and environment with gravity like on Earth. Almost 50% of long period space expedition astronauts develop vision complications. After a study conducted on 15 astronauts that went on a 6 months trip to ISS, scientists found that the tissue surrounding the heads of their optic nerves looked more swollen few weeks after their return to Earth. This is most likely caused by the increased pressure on the eyeball due to the fluid redistribution.

Besides that, the high radiation level also increases the chance of cataract development. More than 39 former astronauts have had some form of cataracts after their space expedition, with 36 of them were involved in high-radiation missions such as the Apollo Moon landings. Usually, cataracts appear in people older than 65 as a natural effect of aging. Some of these cataracts resemble the cataracts astronauts get. link1.

6. Sinuses —nasal congestion

On Earth, the gravity helps in draining your sinuses. The mucus produced is emptied through the nose and down to your throat. In microgravity, the mucus accumulates in your head, giving you the symptoms of a minor cold.

7. Mouth — ‘non-gaseous burps’.

Digestion process in your stomach produces gas, hence the burp. On Earth, the gas in your stomach accumulates at the top of your stomach signaling you to burp. However, in microgravity, the gas in your stomach does not separate from the liquid and solid food. As a result, you may experience unpleasant ‘wet burps’. An attempt to burp may result in vomiting. That is why James Newman, an ISS astronaut, has found a technique to avoid vomiting and ease burping. He did a little push off a wall to enable the gas to move to the direction of his esophagus, and his stomach fluid in the other direction

8. Coordination — Things do not float on Earth!

Astronaut Tom Marshburn holding his cup before releasing it in the air.
Astronaut Tom Marshburn looking for his cup in the air.

Astronauts are so used to things floating in space microgravity and their response and reflexes to moving objects floating like in space. Their reflexes have to be recalibrated once they return to Earth. They are usually more clumsy drop things. Imagine asking them to hand you a mug, and they swiftly throw you the mug!

9. Chance of kidneys stones development.

As mentioned before, astronauts lose bone mass in space. This can lead to a calcium precipitation in the bloodstream that can form kidney stones. NASA evidence shows that astronauts have had not less than 30 instances of kidney stones within 2 years of space travel.

10. Immune system — Bacterial infections and allergic development.

In our immune system, T-cells act as the brain to enable the immune system to recognize pathogens. T-cells are produced in bone marrow. Scientists examined the blood of astronauts before and after space travel, and they found that T-cells reproduction level is lower after their return to Earth. However, scientist are not able to retrieve and study their blood during their space travel. Hence, there is no conclusion to whether the T-cells level is lowered in microgravity or during the re-entry stressful condition.

11. Soft newborn baby feet.

In microgravity, you use ‘handrails’ to move around. You can either use your hands or the top of your feet to hold on to the handrails. After some period of time, the hard skin on the soles of your feet molts off because its not in constant contact with the ground anymore and the top of your feet become raw and sensitive. Astronauts reported that after taking their socks off, they can see the skin particles flies out of their socks. That is why they need to take their garments off in front of a filter to pull the particles into the filter. The bottom of your feet becomes very soft like newborn baby feet.

12. Ageing from 20 to 60 in few months.

Sarcopenia is an age-related muscle loss. It is a natural part of aging. You begin to lose up to 5% of muscle mass per decade after the age of 30. Throughout the course of a lifetime, most men lose about 30% of their muscle mass. The ability to minimize or prevent the effect of this will enable longer and more frequent space expedition in the future.

All these thoughts and talks about space exploration and how it can affect our body, make me wonder about one thing. Humans were made to live on Earth, are we supposed to die here?



Adam Shaari

Physicist | Optics Engineer | Front-end Developer | Writer