Because of the way an acoustic or particularly an electric guitar is played, with an arm draped across the top, sweat and other body oils may cause that area of many guitars to lose their brilliant shine. While there are a number of commercially viable compounds that will restore the shine, the easiest way is by simply putting a small dab of toothpaste on the instrument in the hazy area. Using a soft-bristled toothbrush (or even a soft, lint-free cloth) and just a tiny bit of water, you can usually clear up that murky surface in a matter of minutes.
BE VERY CAUTIOUS when trying this, since too much pressure using toothpaste with too much grit can scratch up that area. Start with an EXTREMELY light touch at first. It’s a good idea to try this on an inconspicuous area of the instrument first, to ensure that there won’t be any damage.
For older guitars with more long-term damage, we suggest you consult a professional luthier who specializes in refinishing or restoring stringed instruments.
Another excellent alternative solution is jeweler’s rouge, which often comes as 4 oz. blocks or even on soft buffing pads in a jar.