ELI5: Explain Like I'm 5

Renal stone formation in space

Renal stones happen when different kinds of minerals and salts in your body come out of the fluid that is in your kidneys. In space, there is no gravity like there is on Earth. Without gravity, fluids in space move differently and can cause more of these minerals and salts to come out of your kidneys. This can then make it more likely that your body will form kidney stones.