It's a common medical myth that white spots on your fingernails are caused by too little calcium in your diet. However, these white spots (called leukonychia) are not a sign of a calcium deficiency. But they can be an indicator of other problems.
The most common cause of leukonychia is blunt trauma to the nail bed, such as a knock or a blow. Due to the slow growth rate of nails, the white spots of leukonychia may appear gradually and linger for months.
Other causes could include a rough manicure, a slight allergic reaction to enamels or other nail products, or even a mild bacterial or fungal infection.
White spots can also appear on toenails, but regardless of their location, they are generally harmless and will disappear with time. However, a nail that turns completely white could be a symptom of liver disease and should be looked at by a doctor