Food allergies: When and how did you develop them?

I was on a different thread and the issue of food allergies came up unexpectedly. Now I'm rather curious. I know people can and do develop food allergies later in life and lose those they had as children; however, are there any warning signs? Why are you one day perfectly able to eat something and a few days later react to it? I suppose personally I'm more interested in food allergies people developed as adults, but I'm sure there are a fair number of people with questions or information about the origin of their childhood food allergies too!

In my particular instance, I found about my apparent food allergy on Chowhound! I can remember having kiwi make my mouth feel as though it had been torn to shreds right around the first or second time I tried it when I was about 10. It also left a weird, metallic taste in my mouth afterward. I liked the actual kiwi taste, but I usually ate it around my sister, who had the same reaction I did. I never realized there was anything odd about this, so I continued to eat it throughout the next 20 or so years. Now it appears that reaction is NOT how people normally feel after they eat kiwi! However, eating the fruit never caused any of the classic food allergy symptoms (like a rash, redness, breathing problems, etc.) for me, so I didn't recognize it as an allergy. To this day I have no other (known!) food allergies.