 Suspected sources of antigens include metals, e.g.cobalt, or additives and preservatives in foods, including benzoates, benzoic acid, cinnamaldehyde, metabisulfates, butylated hydroxyanisole, dodecyl gallate, tartrazine, or menthol, Examples of foods which may contain these substances include margarine, cinnamon, eggs, chocolate or peppermint oil.Some suggest that infection with atypical mycobacteria could be involved, (paratuberculosis), and that OFG is a reaction to mycobacterial stress protein mSP65 acting as an antigen.