Notorious MSG?
It is impossible to be allergic to either sodium or glutamic acid. Allergies are an autoimmune disorder where white blood cells attack substances that are generally not supposed to be attacked; if this was the case for either sodium or glutamic acid, the effects would be immediately fatal given the omni-presence of sodium and glutamic acid, their essential roles in the human body, and given how glutamic acid is naturally produced by the human body.
MeFite Conspire helps to dispel some misinformation in an MSG thread with SCIENCE.