Most of my guitars have had this happen over the years. Sweat and other bodily chemicals react with lacquer and actually soften the surface layer. It doesn't happen on my Taylor because that's got a polyurethane finish. The finish may be compromised all the way through, in which case only a refinish will change it. Definitely not recommended. Under no circumstances should stuff like brasso be used. The safe thing to try yourself is Super Sensitive violin polish, which has some mild abrasive content. If that and a little elbow grease won't do the trick then it's a job for a luthier (I am one). Much as it pains me to have to agree with Clinton, I think he's right on this issue.

Sandy