Look what I just found...
Notice how one label is black and the other is green? Since 2006 O.P.I. has been dibutyl phthalate (DBP) and toluene free. They have never used formaldehyde in nail polish or treatments but does use it in some of their nail hardeners.
Any labels that have green lettering are free from DBP and toluene. Any with the black lettering are older and will contain those ingredients.
DBP was used to help prevent chips and cracks in polish. While toluene (remember how horrible nail polish used smell?) a solvent was used to help make more "spreadable". Both chemicals have many other uses and are still widely used today in things like plastics, adhesives, paint thinner and gasoline.
For additional information please see: