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My experience confirms link between gluten ingestion and canker sores.
 Pre-GF diet I had frequent bouts of canker sores.  Since going GF about 6
months ago, no canker sores, except when I went off the diet for about 1 week
preparatory to biopsy. After 5 days eating wheat again, I got the most
ferocious case of canker sores I ever had.  By the way, Zylactin, which is an
over-the-counter goo that forms a skin over the sores, is the only thing I've
found which brings relief from discomfort and speeds healing.  I should add,
my biopsy was negative.  Nevertheless, I remain GF due to bloating, diarrhea
and canker sores whenever I eat gluten.  Caprylic acid (to control candida)
also helps me.