Problems with nails may be due to
fungus. I know this sounds crazy, but
rub Vicks Vapor Rub on them daily. I saw this in an article by Dr. Gott in our local newspaper. It helped my husband and sister-in-law with their nails. Also, lung problems and smoking affects nails, as it limits the oxygen to the tissue. I am sure their are other medical issues that may affect findernails, but these are the only two that I am aware. Good luck!