This is a good question. Although Maltodextrin is not made from malt or barley it may or may not be gluten free.
It is all dependent on the starch it was made from
e.g maize, corn, tapioca, rice, wheat etc.
Its origin is usually dependent on the country the maltodextrin was made in (sadly this is not required to be stated on packaging).
Watch out for this product as it may be the hidden ingredient that is causing you a reaction.