changes in the shape and texture of nails may tell us of physical problems. Spooning nails, that is when the nail is thin and will growupward along the edges may indicate anemia/iron defiency. Eggshell nails are thin also with the spooning along the edges of the nail may indicate the presence of a chronic condition or a nervous disorder. This may also indicate a problem with chemical exposure, problems with detergents, bath soaps, fingernail polish, malnutrition, and other health problems. It can also be a result of trauma from an accident, tight shoes, ballet, repetitive finger hitting like drumming the finger, or even may be caused by chewing on the fingernails into the quick causing a malforamtion of the nail. The best thing to do is to see the doctor, get some blood work done and go from there. Hope this helps.
Star Queen is right. Changes in mail shape are also ocasionally related to pulmonary sufficiency, curiously enough.