Re: white spots on nails
They're called "Leukonychia" and they can be caused by an injury to the nail, or an underlying infection. They usually surface later than the injury, so by the time see the spot appear you've almost forgotten all about the injury.
Myth is that white spots are caused by lack of Calcium, which is not entirely true. If that were the case, then other symptoms like as Hair loss or Slow Immune system would also accompany the white spots.