In space, no one can hear you sneeze. Though astronauts have been flying above the Earth for more than half a century, researchers are still working to understand the medical toll that space takes on travelers’ bodies and minds. Astronauts must deal with a highly stressful environment, as well as weakening bones and muscles and the ever-present dangers of radiation. If people are ever to venture far from our home planet, such obstacles will need to be overcome. Humans are adapted to living with the constant pull of the Earth’s gravity. Astronauts may seem carefree while floating around in the weightless environment aboard rockets and space stations. But like teenagers, their bodies experience all sorts of awkward changes. Some of the long-term problems, such as bone loss and radiation exposure, seem to put the kibosh on plans for regular interplanetary travel, at least for now. But medical researchers at places like the National Space Biomedical Research Institute are looking for ways to counteract and cure these ailments. In this gallery, Wired takes a look at some of the curious, bizarre, and potentially dangerous ways that space affects the human body and mind. Above: Flying Space Barf Like sailors adjusting to the sea, astronauts usually take some time getting their space legs. During the adaptation to weightlessness, many space travelers’ first experiences include motion sickness, visual illusions, and disorientation. Space adaptation sickness affects about half of all people who have been to space, to differing degrees of severity. Symptoms are jokingly ranked on the “Garn scale,” named after Jake Garn, who flew aboard the Space Shuttle in 1985 and apparently experienced the maximum level of retching and discomfort while adjusting to zero g. Though these symptoms typically pass within a few days, they can be dangerous. Astronauts who don spacesuits need to take anti-nausea medication to combat motion sickness because free-floating vomit inside a spacesuit could be a fatal choking hazard. With several private companies now promising weightlessness during tourist trips to space, the effects of space sickness may start to factor into more people’s lives. After all, who wants to float around in a swanky Virgin Galactic cabin packed with several other passengers and their flying barf? Image: Ellen S. Baker, a medical doctor, conducts a medical examination on astronaut Franklin R. Chang-Diaz on the Space Shuttle Atlantis in 1989. NASA

Foot Molting After initial adjustments, an astronaut's body continues to undergo some strange changes. The weightless environment causes fluids to shift around, mostly flowing into the body and head. This gives astronauts an odd-looking puffy face but can also lead to irritation like nasal congestion. During their long months in space, astronauts’ posture often slouches over into a fetal-like stance, and “standing straight” actually requires conscious effort and strain. One of the weirdest effects happens when the bottom of astronauts’ feet slough off — molting “like some reptilian creature,” as described by astronaut Don Pettit — leaving tender pink skin underneath. This generally occurs mid-mission, after foot callouses have outlived their usefulness since astronauts don’t walk on the ground. Finally, abdominal muscle relaxation from weightlessness leads to a large number of astronaut farts. Image: Astronauts aboard the International Space Station, showing typical puffy faces and upper bodies. Sitting in the front left is Leroy Chiao who appears to have experienced the worst of it. NASA

Bugs in Space Microbes can be found in every crack and crevice on Earth and, apparently, they’ve even colonized space. One test found 234 species of bacteria and microscopic fungi living alongside astronauts aboard the Russian Mir space station. While the majority of these are benign or actually beneficial to humans, there are always a few bad eggs. Astronauts working on Mir between 1995 and 1998 reported significant numbers of microbial infections, including conjunctivitis, acute respiratory illnesses and dental infections. Medical tests revealed that antibiotics are needed in higher concentrations in space and are typically less effective than when used on Earth. Perhaps most disturbing has been finding that the pathogen Salmonella typhimurium became more virulent when living in microgravity. A long-duration mission, like a trip to Mars, only increases the chance for serious infectious diseases to arise and infect the crew. Compounding this danger is the fact that spaceflight does a number on astronauts’ immune systems, making them more susceptible to microbes. In the meantime, researchers are hopeful that antioxidants will prove to be an effective treatment to counteract some of these adverse effects. Image: Scanning electron micrograph of E. coli. NIAID

Bone and Muscle Loss Possibly the most well known effect of weightlessness is the steady deterioration of muscles and bones. On Earth, the human body uses these organs for support and, in zero-g, they suddenly have a lot less to do. Astronauts lose an average of 1 to 2 percent of their bone mass each month in space, causing NASA to consider bone loss one of the primary hazards of long-term spaceflight. As well, muscle mass can vanish at rates as high as 5 percent a week. Making matters worse, calcium from bones leaches out into the bloodstream, where it creates increased risk for kidney stones – a potentially very painful event for an astronaut to endure. And those calcium-deficient bones become very brittle and liable to break, weakening astronauts on long missions. When they touch down back on Earth, some space travelers have to be carried away in stretchers. These numbers are only averages and the actual effects vary greatly. Some astronauts have lost as much as 20 percent of their bone mass in six months. Others get off quite lucky. Cosmonaut Valery Polyakov – the current record holder for time in space – was able to walk from his capsule to a nearby chair after returning to Earth following 438 days in space. An American astronaut said that Polyakov looked “big and strong” like “he could wrestle a bear.” Once back on Earth, bones and muscles return to their former strength. Research suggests that a day of recovery in Earth’s gravity is needed for each day in space. Doctors are also working to combat the weakening, in some cases through hormone therapy. Such treatments may also be able to help people on Earth who suffer from degenerative bone diseases such as osteoporosis. So far, the most effective way that astronauts can work to maintain their pre-spaceflight strength while in space involves diligent exercise. Astronauts aboard the International Space Station currently strap themselves into a special treadmill designed to minimize vibrations that could affect the sensitive microgravity experiments on the ISS. The machine is called the Combined Operational Load Bearing External Resistance Treadmill, or COLBERT, after comedian Stephen Colbert, who had members of his audience write in votes to NASA during a naming contest. Images: 1) Astronaut Ken Bowersox, jogs on a treadmill in the Zvezda service module aboard the International Space Station. The suit was designed to measure stress on lower extremity bones and muscles during everyday activities. NASA. 2) Astronaut Michael Fincke is carried to a medical tent shortly after landing back on Earth in 2009. Though Fincke spent six months in space, he may have been strong enough to stand and getting carried in this way might just be a precautionary measure. NASA

Space Blindness Someday in the future, a fearless crew may conquer all the odds and reach the end of a dangerous eight-month trip to Mars. But as they pull into orbit around the planet, they realize their pilot — and no one on the team — can properly see the controls anymore. Space blindness, for lack of a better term, is a steady degradation of vision that many astronauts have reported. The effect seems to become worse the longer someone has spent in space: Around 30 percent of those on short-duration missions have reported some blurring of eyesight while the number is double for astronauts on long-term missions. The effect has only recently come to light since previous generations of astronauts were scared to report the effect for fear of being grounded. Researchers as yet don’t know the cause of these symptoms but some have suggested they are related to increased fluid pressure in the head pushing the optic nerve into the back of the eyeball. This condition, known as papilledema, can result in permanent vision loss. Blindness is certainly the worst-case scenario, though even blurred vision could badly affect an astronaut and make them unfit for duty, especially on long interplanetary voyages. Image: Jeff Dahl/Wikimedia/Wired Science

Solar Superstorms and Radiation Approximately three months after the crew of Apollo 16 returned from the moon, the sun sent out an enormous explosion from its surface, spewing out radiation and billions of charged particles toward the Earth. This solar storm – one of the largest and most dangerous to occur during the Space Age – thankfully did not occur during Apollo 16 and Apollo 17, which launched four months later. Solar storms and the radiation they create are one of the biggest obstacles to long-term space travel. Outside the Earth’s protective magnetic fields, astronauts are exposed to far more radiation than they normally experience. Solar flares and other bursts from the sun’s surface generate massive amounts of dangerous X-rays and heavy charged particles that can penetrate into the cells of living creatures, damaging DNA and leading to increased risk of cancer. Had astronauts been en route to or on the surface of the moon during the 1972 “superstorm” — or similar events in 1956 and 1989 — they would have experienced massive doses of radiation. Their skin would have burned, blistered, and peeled and the radiation penetrating their bones would have caused nausea and vomiting. In all likelihood, they would have been killed. NASA is required by law to protect its crew from such events and also the longer-term effects of radiation in space. Cumulative exposure in low-Earth orbit – where astronauts receive more radiation than even people working near nuclear reactors on Earth — increases the risk of developing cancer. Since only 24 men have ever traveled beyond low-Earth orbit, the long-term effects of radiation exposure outside the planet’s magnetic field are still largely unknown. NASA guidelines estimate that males should spend at most 268 days in space and females at most 159 days in space to remain below a three percent chance of contracting cancer over their lifetime. A potential Mars mission would take at least 520 days round-trip, during which a dangerous solar flare could occur. Major solar storms have been relatively rare during the last century, though this may not be the case in the future. Data from polar ice indicate that we are living through a relatively mild period of solar activity, which may pick up and cause storms larger than even the largest recorded episode – the 1859 Carrington event – which was approximately four times larger than the deadly 1972 storm. Solar astronomers are hard at work creating better models to help predict such events. Faster computers and increased monitoring might make it possible to forecast solar weather by as much as several weeks in advance. If regular travel to the moon and back ever happens, such data would be extremely useful. Image: Composite of multiple solar flares bursting from the sun. JAXA/Hinode

Toxic Dust Most of spaceflight’s adverse effects come from weightlessness. Once on a rocky body with some gravity, like the moon or Mars, astronauts should get a little relief from degenerative problems and perhaps protection from radiation. Of course, these places come with their own set of strange dangers, primarily from dust. The lunar surface is covered in regolith that is the result of ancient volcanic explosions and meteorite impacts. About 80 percent of the regolith is made up of tiny micron-sized dust particles that have the nasty tendency of sticking to every surface. Lunar dust has properties similar to fractured quartz or silica. Apollo astronauts found it coating the inside of their lunar module fairly quickly, covering their bodies, hair, and spacesuits. If astronauts ever return to the moon, they will have to deal with the microscopic dust particles irritating and abrading their eyes and skin and, worst of all, getting inhaled into their lungs. We still know very little about the toxicity of lunar dust. What we do know is that silica dust on Earth can cause a serious ailment known as silicosis, which once created one of the biggest occupational hazards in U.S. history after dry drilling in a mine in West Virginia killed hundreds of miners during the Great Depression. Finely ground quartz particles are liable to enter the lungs, where coughing does little to dislodge them. The body’s natural antibodies, white blood cells, die when they try to clean up the dust. The reduced gravity on the moon means that dust may float more, be easier to inhale, and stay in the lungs longer. After lunar dust got into the Apollo cabin in 1972, astronaut Harrison Schmitt felt congested and complained of “lunar dust hay fever.” Over long periods, the dust is suspected of acting like asbestos fibers, increasing the risk of cancer for those inhaling it. An even more dangerous scenario is getting exposed to dust on Mars. The Red Planet is red because it is covered in a fine iron oxide dust. Some researchers think that such oxides would corrode organic compounds such as plastics and rubber and leave burn marks on human skin. Windstorms could whip up tiny particles of Mars dust, which would cover everything and work its way through even the finest seams. Future astronauts traveling to either of these places will need to take strict precautionary measures to keep dust out of their base. Image: Astronaut Eugene A. Cernan, Apollo 17 commander, photographed inside the lunar module. His spacesuit is covered in lunar dust as is his skin. NASA