I don't have any real allergies, but when I first had acid reflux, I had to be very careful about spicy foods and caffeine. Any caffeine, especially cola, would send me over the edge. It took about 18 months of being very diligent, but I "cured" myself, i.e. no prescription meds, just a different diet. Now I can have caffeine pretty regularly (although I don't have it every day) and I'm fine. I am more careful about what I eat, but I can pretty much have whatever I want, within reason.
I think that I just needed to detox from all the chemicals and junk in my body. It took a while, but it was worth it. My brother OTOH is still having problems and just cannot get it under control. He keeps "slipping" and having salsa (tomatoes give him big problems) or drinking a beer and he's sick again.
Because the cells in our bodies cycle every 7 years or so, sometimes allergies can come and go. A few months before I turned 28, I started developing a metal allergy. I couldn't wear any earrings that weren't 14K, where I used to be able to pretty much put a stick through my earlobe. About 7 years later, the allergy lessened and now it's almost gone. Now, I can't wear Sterling or copper too many days in a row - my ears get a bit sore and swollen - but I'm generally fine.