This comes via the always fun boingboing – Astronaut nails have a propensity to fall off due to the design of their spacesuits.
In several cases, sustained pressure on the fingertips during EVAs caused intense pain and led to the astronauts’ nails detaching from their nailbeds, a condition called fingernail delamination.
While this condition doesn’t prevent astronauts from getting their work done, it can become a nuisance if the loose nails gets snagged inside the glove. Also, moisture inside the glove can lead to secondary bacterial or yeast infections in the exposed nailbeds, the study authors say.
If the nail falls off completely, it will eventually grow back, although it might be deformed.
I may not be cut out be make it as an astronaut! I rather like my fingernails (and biting them off).