I, for one, have had my share of trouble with nail polish staining my nails, turning them yellow and brittle. Later, I learned that formaldehyde was probably the culprit and to avoid that ingredient when shopping. Even so, my problem occasionally still persisted despite changing different formaldehyde-free brands until I found how best to fix this issue. Here is what I later learned on how to fix polish stained nails to prevent this from happening again.
If you also suffer from disgusting nail stains, you could try soaking your nails in enough lemon juice or hydrogen peroxide to cover. You could even make a paste with some baking soda and try buffing the stain. Do this soaking or buffing only for a few minutes because it is drying and rather brutal to that skin and nails. You must follow up after rinsing everything away with a heavy duty cream or cuticle oil around the nails to normalize them after this treatment.
Another thing that helped this problem was giving my fingernails a rest from polish for at least a month. Once a week I made it a point to file the stains with a two-sided buffer to gradually repair
the damage and return my nails to a healthier state before attempting new polish again.
So if you go without polish, remember exposing your naked stained nails to time in the sun can even help bleach them.
You could also try denture cleanser, which I liked even more with its oxidizing agents to bleach nails. Soaking your nails in denture cleanser for about three to four minutes really helped lift some tougher stains for me.
Then again, I found whitening toothpaste onto the nail beds was amazing for bleaching tough stains as well.
The best piece of advice that I can pass along is always using a wonderful base coat before the thoughts of any polish. Using one will probably be the best thing you can do to prevent those stains in the future.
Unfortunately, I had to discover this the hard way. Hopefully, what I learned about how to fix polish stained nails will at least help you always maintain beautiful nails!