There are many myths surrounding those mysterious white spots on fingernails that occasionally show up, but the simple truth is that the majority of white spots on fingernails are caused by a previous injury to the nail bed. They can be loosely compared to bruises on the skin.
If you notice white spots, also known as leukonychia, on your nails, they are unlikely to have been caused by a vitamin or mineral deficiency. In a few cases, white spots on fingernails can indicate an underlying infection, but much more commonly, they are the result of injury. Similar to bruising, white spots on fingernails do not show up immediately. It may take several days or weeks before you notice the spots.
Because they are generally the result of a minor injury, you are likely to have forgotten all about banging your fingernail against the car door.