To truly test whether you have the right stuff, imagine ripping out your own fingernails, on purpose. A couple of astronauts have done this before going into orbit, because they figure it’s better than losing them inside chafing, unwieldy spacesuit gloves [...]
Fingernail trauma and other hand injuries are spacewalkers’ biggest complaint, she said. In a recent study of astronaut injuries, at least 22 reported lost fingernails, a phenomenon called fingernail delamination. It happens because of pressure on the fingertips, but researchers also think circulation cutoff could be to blame.
I am surprised that this was not in the new Mary Roach book.