Hi -
long time since you posted the question, and I don't know if this is the answer, but the cold-sore might have been a detoxification reaction. I once had this happen with grapefruit seed extract. I read about its detoxifying properties and initially took too much (ie beyond the recommended 10 drops or whatever it was) and woke up the next day with a massive coldsore. I returned to the health food store and the woman who'd recommended it yelled at me for not listening to her (! this was in Italy as well) and said, these extracts aren't just for fun, they have powerful reactions in the body. Your cold sore was your body's elimination of the excess extract. I could see your reaction to a first-time use of DE as an analogous reaction. In fact, I've started taking it only recently, but realized I needed to start with less than a tablespoon, and even alternate days or weeks according to, well, my intuition. But the same sense of intuition, from day 1, told me -- don't stop taking this stuff.