working on iss toe holds
Expedition 43 commander and NASA astronaut Terry Virts is seen here closing the hatch to the Leonardo Permanent Multipurpose Module with his feet strapped in to foot loops.
NASA Johnson/Flickr
Since they're not walking around on the ground under the force of gravity, astronauts don't have to wear shoes in space.

They usually just wear socks and layer on a second pair of warmer socks if they get cold.

But Astronaut Scott Kelly, who's spent almost a year in space, said in a Reddit AMA that this made something rather odd happen to his feet.

"The calluses on your feet in space will eventually fall off," he wrote. "So, the bottoms of your feet become very soft like newborn baby feet. But the top of my feet develop rough alligator skin because I use the top of my feet to get around here on space station when using foot rails."

Kelly also said in a Q&A on Tumblr that this foot phenomenon was the "weirdest thing" that had happened to him on the ISS.

Astronauts on the International Space Station (ISS) use foot rails and loops to help hold them steady when they have to do an experiment, or just get a haircut.

NASA Astronaut Kjell Lindgren gives Russian cosmonaut Oleg Kononenko — who has his feet planted under the foot rails — a haircut inside the ISS.
NASA Johnson/Flickr
When they want to work out, astronauts can strap their feet into sneakers on the exercise equipment.

Astronauts typically only change their socks and underwear every other day, and their shirts and pants every 10 days, according to NASA, since they don't get as dirty in space as we do here on earth.

Astronaut Don Pettit, who's logged over 300 days in space, said the same thing happened to his feet in a 2012 blog post.

"After about two months in orbit your feet molt, and like some reptilian creature the callused skin on the bottom of your foot sheds, leaving soft pink flesh in its place," he wrote. "In the weightless environment, calluses apparently have no use, at least on the bottoms of your feet. However, the tops of your feet become red-rubbed raw and gnarly. And the bottom calluses shed faster than the top calluses can grow. Perpetually raw and hypersensitive, your foot tops can use a bit of padding to ease the pain."

Astronaut Don Pettit showing off his toe koozies.
Don Pettit/NASA
But Pettit found the perfect antidote to his lizard skin, which he called "toe koozies."

He accidentally grabbed a pair of small women's socks one day that only covered the top half of his foot, but they perfectly protected the part that needed it.

"They are the zero-gravity equivalent to flip-flops," he wrote.