Some of the causes of white marks are liquids containing alcohol (perfume, medicine, beverages), heat and water. Your success in removing such marks depends on the amount of damage and its cause. The following treatments may be helpful in minimizing or removing such marks.
Many spots will disappear if rubbed with a solution made of equal parts of boiled linseed oil, turpentine and vinegar, or with a cleaning-polishing wax. If the mark is stubborn, rub with 3/0 or 4/0 steel wool instead of a cloth. Rub with the grain of the wood. Do not use steel wool on high gloss finishes. Turpentine is flammable so follow cautions for solvents: no flame or spark nearby, do not get on skin, do not breathe.
Rub spot lightly with a paste of powdered pumice or rottenstone and linseed oil.
Spots on all finishes except lacquer can be treated with a cloth dampened with spirits of camphor, essence of peppermint or oil of wintergreen. As these may make the surface tacky, do not rub. When dry, you may need to smooth the roughened spot by rubbing with a paste of powdered pumice or rottenstone and linseed oil.
Alcohol spots often respond to a quick exposure to ammonia. Rub lightly with a cloth dampened with non-sudsy water and a few drops of household ammonia.
Not all treatments will work on all finishes. When completed, wax/polish entire surface. If spots cannot be removed, refinishing may be necessary.