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