On the basis of applying the IFBC/ILSI decision tree in a number of cases, a refinement of the scheme is suggested. Large differences in allergenic potential may be obtained by altering the route of administration of an allergen. Because an inhalation allergen can induce symptoms at different threshold doses depending on whether it is introduced via the inhalation or oral route, we propose that double-blind, placebo-controlled food challenges be performed in all cases of inhalation allergens being present in foods. Even proteins never previously ingested may cause IgE binding and elicit clinically relevant symptoms.