Why space is not a great place to be

Living in a world with microgravity where you're just inches from exposure to the vacuum of outer space can have a profound influence on the human body. Most astronauts only spend six months at a time in that environment on the International Space Station (ISS), floating 250 miles above the Earth. Scientists know a few things about what a six-month stay in microgravity does to the human body, some of which are downright disturbing.

It stretches out your spine

Astronauts can grow up to 3 per cent taller in space. That means that a 6-foot-tall astronaut could tack on an extra two inches. The growth spurt happens because microgravity allows the soft spinal discs between vertebra freedom to relax and expand. It takes a few months to return to normal height after they get back to Earth.

It turns your muscles into jelly

You don't need muscles to support you in a weightless environment. Astronauts' muscles almost immediately start shrinking and shedding the extra tissue that they no longer need. As such, exercise is crucial on the ISS, so astronauts can maintain the muscle mass they need when they return to Earth. They usually budget about two hours a day for exercise.

It makes your face puffy
Our bodies are mostly liquid. The gravity on Earth pulls that liquid down and some of it pools in our lower extremities. In near zero-g, the liquid is spread out more evenly around the body, so astronauts' faces look puffier than normal while their legs look skinnier than normal. After a few weeks the body adjusts to the gravity change and some of the puffiness goes away.

It thins out your bone density

Astronauts can lose around one per cent of their bone density every month they spend in space if they don't regularly exercise. It makes them a lot more likely to break bones when they're back on Earth — similar to people who have osteoporosis. Exercise and good nutrition is crucial for minimising this effect.

It can cause vision problems

A 2013 study examined the eyes of 27 astronauts who had spent an average of 108 days on board the ISS. NASA researchers found that many of them had eye abnormalities after returning from space. MRI scans showed that nine of the astronauts had bloating around their optic nerves and six of the astronauts had eyeballs that were physically flattened out in the back. This is definitely cause for concern, but none of the astronauts have reported any serious trouble seeing.

It messes with your immune system

Living in space can depress astronauts' immune systems, according to a study published in 2014. "Things like radiation, microbes, stress, microgravity, altered sleep cycles and isolation could all have an effect on the immune system of crew members," Brian Crucian, NASA biological studies and immunology expert, who led the study, said in a statement. "If this situation persisted for longer deep space missions, it could possibly increase risk of infection, hypersensitivity or autoimmune issues for exploration astronauts."

It upsets your sleep cycle
Astronauts have to strap themselves into sleeping bags every night. In microgravity their heads roll forward and their arms float up once they fall asleep. The weird position is hard to get used to. There are also other disturbances that make it challenging to get quality sleep in space. Brilliant fl ashes of light that can illuminate the space station every time streams of cosmic rays shoot by. Now, astronauts have individual sleeping pods that help shut out some of that light.

It messes with your senses

Pressure changes in space and so fluids shift around in the body. The same effect that makes astronauts' faces puffy also makes them congested. "It's the same as having a cold or allergies," astronaut and physician Scott Parazynski told Scientific American. Many astronauts have reported that flavours are much more dull in microgravity, so they crave food with a lot of extra flavoring and spice to make up for the bland taste.