It can be pretty severe. It really depends on how much MSG I eat at a time. I can eat a small bag of chips seasoned with msg and not have much of an issue, but eating a full meal with msg in it,is pretty much out of the question. The biggest issue with my allergy is the symptoms them self's. Its not what you would call a normal foodallergy symptoms. It gives me some insanely bad migraines and debilitating motion sickness. I can take medications for it but only after I have eaten food with msg. There currently is no preventive med's for it. I think I'm just going to have to keep my med's on me and hope for the best.