Normally, to survive in space outside of a sealed spaceship you need a bulky full-body space suit. Not necessarily the case in TV land. Earlier audiences might be expected to know that there's nothing to breathe in space, but before Explosive Decompression became a common trope writers might have supposed they could get away with putting a scuba mask on their characters.
Needless to say, in real life, an oxygen mask alone is nowhere near sufficient to protect someone from space. Decompression may not be as dramatic as it often appears in Hollywood, but it's still not pretty, and probably not survivable for extended periods. This is because spacesuits need to keep our bodies under enough air pressure for our bodily fluids like blood to remain in a liquid state. Once we pass the "Armstrong Limit" (a point where air pressure is low enough for water to boil at human body temperature), unprotected spacewalks will become fatal in 60-90 seconds. In addition, space is full of deadly radiation from solar winds and cosmic rays, and exposing your body to that will cause serious radiation illnesses and cancer.
Alternatively, putting a simple mask over one's mouth and nose while retaining the rest of the character's normal costume might make them easier to recognize, compared to a full-body spacesuit. Or they might need to conserve assets for a CGI work.
See Batman Can Breathe in Space for when you don't even need an air supply. May take the form of a Fishbowl Helmet. Compare Latex Space Suit for another form of minimalistic space wear. Not to be confused with Space Suits Are Scuba Gear, which is when a full-body space suit has vulnerable external air hoses.
- Burning Through Space 2: The Red Team has to battle an alien armada outside of their spaceships and all equip helmets and jetpacks, but no actual spacesuit for their bodies. Scout even Lampshades how cold it is out in space.
- Rocketship Voyager.
- During the climatic battle against the Psiborg Collective, Captain Janeway steps out of an airlock wearing only an oxymask because she doesn't have time to put on space armor. Janeway fires a rocket-grapple to save B'Elanna Torres' life, only to drop the launcher as her fingers swell up because the fluids in her body have started to boil in the vacuum. B'Elanna quickly shoves her back into the airlock and seals the hatch behind them.
- Earlier when the docking bay of the Psiborg cube-ship starts to decompress, a liquid gel flows across the face of the Psiborg holding Janeway prisoner, sealing its mouth and nostrils, while tubules from an air tank on its back inject oxygen into its neck.
- In The Empire Strikes Back when Han, Leia, and Chewie go outside the Falcon to investigate the strange noises coming from the asteroid cave they're hiding in, they simply put on masks connected to tanks on their belts.
- Guardians of the Galaxy (2014): Star-Lord wears a metal mask that only covers his face and retracts behind his ear when he's not in open space. The sequel replaces it with full-body force fields.
- In The Andalite Chronicles Andalites wear "air hoods" for space walks that are described as essentially clear plastic bags attached to a gas canister and which go over the head. The gas mixture in the canisters is not only oxygen but a blend of other unnamed gases that somehow compensate for the effects of decompression. Unfortunately for Loren the mix is calibrated to Andalite physiology but not for humans and she's in intense pain while wearing one.
- Agents of S.H.I.E.L.D.: When introduced aboard the Lighthouse space station in the Season 5 premiere, Deke is wearing a mask like Star-Lord's mentioned above.
- Doctor Who: In "Four to Doomsday", the Doctor does a spacewalk from the Urbankan ship to the TARDIS wearing a highly advanced space helmet, which emits a force field to protect him.
- For All Mankind: In the season 2 finale "The Grey", Gordo and Tracy Stevens are forced to improvise spacesuits out of duct tape and gas masks to go out onto the lunar surface to repair Jamestown's reactor coolant system. Without oxygen or actual radiation protection, it keeps their bodies together for at most one minute and they barely return to the airlock before dying of exposure.
- Deconstructed in FTL: Faster Than Light. The "Emergency Respirators" Augmentation only halves the damage the crew takes from being in vacuum. They can breathe, sure, but without a pressure suit to go with it, they still get hurt.
- Mass Effect: In the first game, Shepard and all squadmates will wear full helmets whenever walking around in the vacuum of space or on worlds with extremely low atmospheric pressure. In the second and third games, however, certain squadmates will wear only a breather mask covering the nose and mouth (or, in Javik's case, eschew any kind of facial covering entirely). Though possibly justified in that the squadmates who don't wear helmets are generally either biotics (so it's possible that they're simply using a biotic field to protect them) or robots, but overall it's very clearly trying for an Acceptable Break from Reality so that their faces are more readable (case in point: Shepard's helmet leaves only the eyes visible, greatly limiting how expressive they appear to the player).
- Metal Slug: The third game's final level, prior to the Battleship Raid, has a segment where players get on an Astro Slug and battle Martians in the depths of space. If the rockets end up being destroyed while in space, the player then continues the mission wearing a Fishbowl Helmet connected to an oxygen tank, in their regular army uniforms without a spacesuit.
- Zig-Zagged throughout the Ratchet & Clank series: whenever Ratchet has to go out in the vacuum of space, he'd either don an O2 mask, or his helmet would extend to cover his full face. Same goes for underwater levels. Either way, his body and large ears may still exposed to the vacuum depending on what helmet and armor he's wearing.
- Henry Stickmin Series: In the Jewel Baron route of Completing the Mission, Henry screams so loudly that he shatters a window in the Toppat Space Station, which sends him and Right Hand Man into space. Right Hand Man tries to put on the oxygen mask from his hat, but Henry bumps into him and he drifts off into space. Henry puts on the mask to survive.
- Super Paper Mario: In Chapter 4-1, Mario, Peach, and Bowser end up in outer space unprepared, nearly suffocating from lack of air before Tippi teleports them back to Flipside. They later return with a makeshift space helmet they can breathe in, which is just an ordinary goldfish bowl they borrow from a kid.
- In The Avengers: Earth's Mightiest Heroes all Hulk needs when going into space is a facemask and oxygen tank. He does wear a more durable set of shorts than his normal torn purple pants.
- Invincible: Invincible just holds his breath the first time he goes into space, but for the weeks-long trip to Mars, he wears a faceplate attached to an oxygen tank.
- League of Super Evil: Anytime a character is underwater or in space, all they need to survive is a helmet.