Frequent application of nail polish may also result in yellow nails caused by staining. It is recommended to let the nails breathe often and to avoid wearing nail polish for long periods of time. Wearing nail polish for too long may cause nail fungus. The pigments used in nail polish, particularly darker shades, can stain your nails over time. The best way to prevent this is to use a breathable nail polish special for nails with nail fungus or to use a clear-base coat before applying a nail polish.
Other causes of nail discoloration can be chronic liver disease, excessive smoking and poor lifestyle habits.