A myriad of different symptoms can be associated with IgE-mediated food allergies; these symptoms develop within minutes to a few hours. The symptoms that occur during a food-allergic reaction will not always be the same. The nature of the symptoms and their severity depend upon several factors including the individual, the amount of the offending food ingested, the tissue receptors that are affected, and the length of time since the previous exposure. Some individuals tend to develop only mild symptoms while others may experience much more severe manifestations.
The symptoms of IgE-mediated reactions can involve the gastrointestinal tract, skin, or respiratory tract. Gastrointestinal and cutaneous symptoms are among the more common manifestations of IgE-mediated food allergies. Common gastrointestinal symptoms include abdominal cramps, nausea, vomiting, and diarrhea. Of course, all of the GI symptoms have multiple possible causes and can occur in other foodborne disease. The diagnosis of food allergy based upon the appearance of gastrointestinal symptoms alone can be quite difficult.
Cutaneous symptoms will include hives, itching, and eczema or dermatitis. Dermatitis is an especially common manifestation in early childhood. About 40% of cases of dermatitis in young infants may involve food allergies.
Respiratory symptoms are much less commonly encountered in food allergies. However, individuals with respiratory manifestations of their food allergies can be more likely to experience severe and life-threatening reactions. Mild respiratory symptoms (rhinitis, rhinoconjuncitivitis) are much more likely to be encountered with exposure to environmental allergens such as pollens or animal danders that are airborne and inhaled directly into the respiratory tract. While these mild respiratory symptoms are mostly annoying, those few food-allergic individuals who experience serious respiratory manifestations (asthma, laryngeal edema) in association with the inadvertent ingestion of the offending food are most likely to be at risk for life-threatening episodes.
Anaphylactic shock is the most severe manifestation of IgE-mediated food allergy. Anaphylactic shock can involve multiple organ systems (gastrointestinal, respiratory, cutaneous, and cardiovascular) and numerous symptoms. Death can ensue from severe hypotension coupled with respiratory and cardiovascular complications. Anaphylactic shock is a common cause of death in these fatalities.
Some symptoms of food allergy are potentially quite severe. As noted above, anaphylactic shock is the most severe. But, asthma and laryngeal edema can also be very serious symptoms. Fatal reactions can and do occur. Death can ensue from severe hypotension coupled with respiratory and cardiovascular complications. Comparatively few individuals are susceptible to suffering such severe reactions upon food ingestion. The inadvertent ingestion of allergenic foods has resulted in deaths. Deaths have occurred with most of the common allergenic foods (all of the Big 8 except wheat), although peanuts, tree nuts, and crustacea seem to be more frequently implicated in severe food allergies than some of the other commonly allergenic foods. The prevalence of severe allergic reactions to foods is rather uncertain. The number of deaths occurring from IgE-mediated food allergies in the U.S. (or in other countries) is somewhat debatable. Some experts have estimated that 100 - 200 deaths occur each year in the U.S. However, many of these deaths are not recorded as food allergy deaths because of the nature of the reporting systems used by the U.S. health care community. Certainly, fatal reactions can and do occur. The precise number may not be as important as the realization that fatal food-allergic reactions are preventable.
In conjunction with the growing prevalence of food allergy, the number of patients hospitalized due to food allergic reactions has also increased from an average of 2,600 patients discharged per year between 1998-2000 to 9,500 per year between 2004-2006 (Branum and Lukacs, 2008; Sampson, 2003). Unfortunately, there is no treatment currently available to cure food allergies, so patients must follow strict avoidance diets to safeguard against adverse reactions.
Oral allergy syndrome
Perhaps the most common and possibly the most mild form of IgE-mediated food allergy is the so-called oral allergy syndrome (OAS). OAS symptoms are confined to the oropharyngeal area including itching, hives, and angioedema. OAS is most frequently associated with the ingestion of various fresh fruits and vegetables. OAS is an IgE-mediated reaction to specific proteins present in fresh fruits and vegetables, even though fresh fruits and vegetables contain comparatively low amounts of protein. These fruit and vegetable allergens are apparently quite susceptible to digestive proteases in the gastrointestinal tract, thus systemic reactions are rarely encountered to these foods (important exceptions do occur). These fruit and vegetable allergens are also apparently heat-labile, since the heat-processed versions of these foods are not typically involved in initiation of OAS. With OAS, affected individuals are initially sensitized to one or more pollens in the environment, such as birch and mugwort pollens, that cross-react with related proteins found in the fresh fruits and vegetables. With OAS, sensitization to the pollen increases the likelihood of sensitization to specific foods. Birch pollen allergy is quite common in northern Europe due to the high density of birch trees. Some individuals with birch pollen allergy are also allergic to fresh apples, raw hazelnuts, and some other fresh fruits and vegetables. OAS appears to be somewhat less common in the U.S. but an example of OAS in the U.S. is itching of the mouth (or other mild OAS symptoms) from ingestion of watermelon in individuals with ragweed pollen allergy.
Exercise-associated food allergies
Exercise-associated food allergies are a subset of the immediate hypersensitivity reactions to foods. In these cases, exercise must be done coincident with ingestion of the food for symptoms to occur. Of course, in many individuals, food allergy occurs in the absence of exercise. And, it is also true that exercise-associated allergies can occur that are not related to food ingestion. Exercise-induced food allergies have been associated with numerous foods including shellfish, wheat, celery, and peach. The symptoms of exercise-induced food allergies are individualistic, variable, and similar in nature to those involved in other food allergies. The mechanism of this illness is not well understood, although the involvement of IgE antibodies is apparent.
- Branum AM, Lukacs SL. 2008. Food allergy among U.S. children: trends in prevalence and hospitalizations. NCHS Data Brief:1-8.
- Sampson H A, 2003. Anaphylaxis and emergency treatment. Pediatrics 111:1601-8.