The overall and worldwide prevalence of IgE-mediated food allergies is not precisely known. In the US, the overall prevalence of IgE-mediated food allergies would be estimated at 3–4% of the population. The prevalence is highest in infants and young children ranging from 4–8% in that age group, while that in adults is probably about 2–3%.

Recently, the estimate of the prevalence of IgE-mediated food allergies in adults in the US has been increased, based upon a survey that indicates that 1.9% of the total population has shrimp/crustacean shellfish allergy and 0.4% of the total population has fish allergy; both fish and crustacean shellfish allergies affect many adults.

These percentages are added to earlier estimates that peanut and tree nut allergies affect an estimated 1.1% of the US population, including many adults. Cows’ milk, eggs, and peanuts are among the most common allergenic foods for infants and young children.

While crustacean shellfish, fish, and peanuts are among the most common allergenic foods for adults in the US. Although the situation can vary in other countries depending upon dietary eating patterns. IgE-mediated allergic reactions involve numerous symptoms ranging from mild to life-threatening.

Food-allergic individuals experience quite varied symptoms and it is likely that no one suffers from all of the symptoms. The nature and severity of the symptoms may also vary from one occasion to another in the same individual as a result of the amount of the offending food ingested and the length of time since the last previous exposure.

Anaphylactic shock is the most severe symptom for IgE-mediated individuals. Fortunately, comparatively few food-allergic individuals are susceptible to such severe reactions. Systemic anaphylaxis involves many organ systems and numerous symptoms together with cyanosis, chest pain, and shock.

Anaphylactic shock and asthma are the most common causes of death in the occasional fatalities associated with true food allergies. Although severe, life-threatening reactions are definitely the most worrisome manifestations of IgE-mediated food allergies, mild symptoms are much more likely to occur.

One of the more common and typically most mild forms of IgE-mediated food allergy is the so-called oral allergy syndrome (OAS). In this condition, symptoms are usually confined to the oropharyngeal area of the mouth and throat and include pruritis, urticaria, and angioedema.

OAS is most frequently associated with the ingestion of various fresh fruits and vegetables. Even though fresh fruits and vegetables typically contain low amounts of proteins, OAS is an IgE-mediated reaction to specific proteinaceous allergens present in these foods.

These fruit and vegetable allergens are apparently quite susceptible to digestive proteases in the gastrointestinal tract. Systemic reactions are not typically encountered in OAS, but can be with certain patients and certain foods, e.g. celery. These 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 pollens in the environment, such as birch and mugwort pollens, that cross-react with related proteins found in the fresh fruits and vegetables. Apparently, sensitization to these pollens can increase the likelihood of sensitization to specific foods.

Occasionally, food allergies occur in conjunction with exercise. The prevalence of exercise-associated food allergies is unknown. In these cases, the exercise must be preceded or followed by the ingestion of specific foods in order to elicit an allergic reaction.

Shellfish, wheat, and celery are among the foods that have been incriminated in food-dependent, exercise associated anaphylaxis. The symptoms in this type of food allergy are individualistic and similar to those involved in other food allergies. With increased awareness of the existence of this syndrome and the emphasis on physical fitness in many countries, reports of this condition may continue to increase.