—say, you were walking barefoot one too many times in your gym’s locker room—can blacken your toenails, says dr. lepow. it’s also possible that blackening under your toenails can simply be a natural pigment change as you get older. while some causes of black toenails can be serious,...
Black toenail fungus is caused by dermatophytes, and causes color changes, thickening, and separation of the nail from the nail bed.