Abstract
Food allergic reactions primarily occur after exposure to the offending food through ingestion, contact, or inhalation. However, it can occur covertly through hidden ways that are often missed, with undesirable consequences. Information has been accumulating over the years to indicate that food allergy (FA) may have been the problem in subjects who do not report an association to eating, touching, or smelling a food. Therefore, it would be prudent to explore the possibility of a hidden FA. The causative substance may be a food allergen or a nonfood allergen hidden in a previously tolerated food. Food allergens are commonly hidden in various medications, even in anti-allergy drugs. A blood product may passively transmit food allergens to a recipient who is sensitized or food-specific immunoglobulin E antibodies to a recipient who is nonatopic. It may also be excreted in breast milk, saliva, or semen. Transmission of the FA genetic trait can occur through transplantation of hematopoietic tissue. When the medical history and routine allergy evaluation do not point to the cause of an allergic reaction, it would be prudent to suspect hidden FA before labeling the reaction as idiopathic. A skillful detailed history taking, a cooperative patient, a careful reading of labels, and an interested allergist are needed for suspecting hidden FA and for planning an appropriate evaluation and verification of the offending allergen and, ultimately, optimal relief for the patient.