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I found that gluten-containing foods give me canker sores, and so I
have sworn-off every gluten I can think of.  Now I never get canker
sores on the lips and that is a huge improvement.  However, I
notice that maybe every two weeks or so I get a canker sore on the
inside of the cheeks.  I have been putting this down to something I
ate, like too much salt on popcorn, or too much chocolate.  It
occurred to me recently that maybe gluten, for people who can't
tolerate it, causes the sores to break-out on the lips while some
other agent(s) cause the sores to break-out on the cheeks.

Of course the sores on the cheeks are often precipitated by me
accidentally biting my cheek.

Perhaps the surfaces of those different sites are sensitive to
something produced by the particular agent, but not by the other
agent.

Has anyone else thought the same?

Tom Fitzsimmons.