Common items like salt and bread are banned from the International Space Station due to fears that they'll send floating pieces everywhere and potentially damage space equipment or accidentally get inhaled by astronauts.
Basic eating, sleeping, and showering habits must also be modified.
Astronauts make a lot of sacrifices when they venture off of Earth.
Besides the dangers of space travel and time away from family, microgravity comes with a whole new set of rules that dictates many facets of everyday life.
Here are nine things astronauts can't do in space.
Astronauts can't cry the same in space as they do on Earth.
Astronauts can laugh in space all they want, but the act of crying is quite different without gravity.
When asked if he could cry in space, Canadian astronaut Chris Hadfield answered, "Can you cry in space? Your eyes make tears but they stick as a liquid ball. In fact, they sting a bit. So — space tears don't shed."
Unless an astronaut wipes that water away, tears in space can form a giant clump that can break free of your eye, as The Atlantic explained. So in space, you can actually watch a ball of your tears float around.
They can't consume common items like bread and soda.
Bread, for example, can result in crumbs that can damage equipment or accidentally get inhaled by astronauts. Therefore, according to NASA, tortillas have been used since the 1980s.
When it comes to beverages, carbonated drinks are off the table because they aren't buoyant in a weightless environment. Vickie Kloeris, Subsystem manager for Shuttle and ISS food systems at Johnson Space Center and program manager for NASA FTCSC,told NASA, "carbonated drinks currently don't make the trip because the carbonation and the soda will not separate in microgravity."
Salt and pepper have also been banned for their ability to float away and potentially damage equipment or get in astronaut's mouth, ears, or nose. Thankfully, NASA has developed liquid versions as a substitute.
According to Space.com, the only people ever to enjoy bread in space were the astronauts on NASA's 1965 Gemini 3 mission — John Young smuggled a corned beef sandwich onboard.
Astronauts can't write with regular pens.
If you've ever tried to write with a pen upside down, you'll know that it doesn't work. The ink needs gravity to flow. According toScientific American, astronauts from the US and cosmonauts from Russia both originally stuck to mechanical pencils in space.
Then in 1965, the Fisher Pen Company patented a pen whose cartridge is pressurized with nitrogen. That pressure pushes the ink toward the tip, allowing the pen to work even when upside-down, in extreme temperatures, or underwater. The pens are still used today.
They can't coordinate their sleep schedules with the rising and setting of the sun.
On the International Space Station, astronauts can experience up to 16 sunsets in a 24-hour day. So their sleep schedules can't rely on light patterns.To prepare for this, astronauts go through intensive sleep training before they launch, according to Space.com.
Drinking alcohol is not allowed in space.
Although sherry was once proposed in 1972 as a part of astronauts' meals, it never made it to the space station due to public outrage over astronauts drinking in space, and created the need for an alcohol ban.
Daniel G Huot, spokesperson for Nasa's Johnson Space Centertold the BBC, "Alcohol is not permitted onboard the International Space Station for consumption." But Russian cosmonauts are apparently allowed to consume Cognac for immune health.
The reasoning, however, doesn't have much to do with science.
"It's a political thing. It's a cultural thing. It's not a scientific thing," Dave Hanson, a professor emeritus of sociology at the State University of New York at Potsdam told the BBC.
Sex is banned on space missions. So far, the space station does not admit to knowing about any sex that has happened in space.
As Slate points out, it would be incredibly difficult to have sex in space, given astronauts' lack of privacy, overwhelming workloads, and lack of gravity.
They can't enjoy a hot shower.
In space, astronauts must use all resources — especially water, which is heavy and therefore expensive to transport — as efficiently as possible. In place of showers, astronauts take sponge baths using water distilled from humidity in the air, urine, from oral hygiene, and hand washing, among other things.
On the ISS, according to NASA, water is gathered from humidity in the air and from human waste to be turned back into purified drinking water. There also isn't a particularly efficient way to wash clothes, so astronauts just repeat outfits.
Astronauts can't taste as well while in space.
NASA reports that astronauts can start to lose their sense of taste while in space. Once back on Earth, they say foods taste much stronger.
One reason for this might be that in space, fluids in the body move differently because of the lack of gravity. So rather than being needed in the legs, fluid in the body goes to the head, where it can stuff up the nasal passages. Another hypothesis is that strong odors in the cabin of the ISS dull the body's sense of smell, which in turn, dulls the sense of taste.
Pooping in space is very difficult.
"Number two ... is more challenging because you're trying to hit a pretty small target," Peggy Whitson who spent a record 665 days in space, previously told Business Insider. The bathroom (if you could call it that) also has no door — just a curtain — and astronauts must strap in so they don't float away.
The lack of gravity can cause some unsavory complications, since even pieces of human waste can float away. Here's how astronaut Barry Wilmore once described it:
"Using a fish metaphor, there was a very rare occasion when, sometimes, product gets away, and the term was 'brown trout.' So you have to re-corral your brown trout. And that can be kind of humorous. You go, 'This stuff doesn't happen on Earth.'