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Yes, what she said, because there are hidden sulfites in those kinds of salts. Some of it is the anti caking agents, too. I would think you would be better off with either fresh garlic or with only the garlic powder. It isn't that much effort to use the garlic powder and add your own salt. Besides, you get more bang for your buck to get single herbs and spices, and you have more control over how much salt you are using if you blend it yourself. My mother used to buy the stuff with the salt already in it. I learned a long time ago that that stuff is simply too salty. It's more salt and anti caking agent than it is the actual garlic. A mortar and pestle will make your own salt fine and powdery if that is a concern when making your own. It never bothered me to that point, though, when adding my own salt.
Also, when you add your own salt, you can avoid the table salt that has the additives and you can add a healthier form of salt. Real salt is a great sea salt that still has the trace minerals in it. It comes from the salt beds in Redmond, Utah. It almost looks like the salt has flecks of pepper already in it. But, that's just the trace minerals. For most ordinary food, this natural coloration in the salt should prove to be no problem once you're used to it. It also tastes less salty than the table salt stuff out of the canister. I like it better, because it doesn't bother my stomach.
The best way to figure out for sure is to use the information you have from the allergist and stay away from garlic and onions both for several weeks. Then go back to eating one meal with the garlic in it.
Do go on an elimination diet first, though, for about six weeks. In your case you will have to eliminate garlic and onions through the elimination diet phase meant to bring the body to a more neutral state before challenging the food in question.
Since you're already noticing symptoms in your case, I would go on the elimination diet first as I mentioned, then go to the allergist's office with a head of garlic or a meal prepared with all other foods that you know you're okay with but has garlic in it, as that is the food in question. Do so with the allergist in the room with you and your husband. Relax the best you can while you're in the room waiting to see if you'll have a reaction. A good allergist will be prepared for emergencies if you do have a serious life-threatening reaction.
I think there is a strong likelihood that you have developed a stronger allergy than what you tested at just three years ago.