Food Allergy: What You Need to Know

Stephanie A. Leonard, MD


November 15, 2010

In This Article

Clinical Manifestations of Food Allergy

Reactions to food can occur with very small amounts of exposure and develop in minutes or up to 2 hours after ingestion. Symptoms can be cutaneous, gastrointestinal, respiratory, circulatory, neurologic, and/or atypical, such as a metallic taste in the mouth (Table 1).

Table 1. Symptoms of an Allergic Reaction

Organ System Symptoms
Skin Pruritus, flushing, urticaria, angioedema
Gastrointestinal Oral pruritus, abdominal pain, cramping, vomiting, diarrhea
Upper airway

Lower airway

Sneezing, nasal congestion, coughing,
hoarseness, throat pruritus/tightening,
difficulty swallowing

Wheezing, shortness of breath, cyanosis, respiratory arrest
Cardiovascular Early tachycardia, late hypotension, dysrhythmia, bradycardia, cardiac arrest
Neurologic Change of activity level, anxiety, feeling of doom, dizziness, loss of consciousness
Other Metallic taste in mouth, uterine cramping, urinary urgency

About 90% of reactions present with cutaneous, 70% with respiratory, 30%-45% with gastrointestinal, and 10%-45% with circulatory symptoms ranging from palpitations to collapse.[4] Severe reactions are predominantly respiratory in children and circulatory in adults.[38,39]


Anaphylaxis, by definition, is a severe multiorgan system allergic reaction that can be fatal.[40] Anaphylaxis can progress rapidly without cutaneous symptoms. Although anaphylaxis is usually uniphasic, biphasic reactions can occur in up to 20% of cases, and protracted reactions have been reported.[41] In a biphasic reaction, symptoms typically recur within 1-4 hours after apparent resolution of the initial event, although recurrence as late as 72 hours after exposure has been reported. Biphasic reactions occur more frequently when the initial administration of epinephrine is delayed and are rare after mild initial reactions. Rarely, protracted anaphylaxis can persist for several days, with multiple recurrences interrupted by asymptomatic periods lasting hours.[42]

Contrary to a commonly held belief, allergic reactions do not automatically get worse each time. However, previous food-induced anaphylaxis does put a patient at risk for future anaphylactic reactions.[42] A number of factors influence reaction severity such as the amount of allergen ingested, how the food was prepared (raw vs heated), the amount and type of other food ingested, the presence of acute viral illness, the status of an underlying chronic disease, alcohol consumption, and exercise.[43,44]

Risk factors for fatal anaphylaxis include adolescence, a history of asthma, a history of anaphylaxis, delayed or no epinephrine received, cardiopulmonary disease, an upright posture during the reaction (mostly in adults, leading to empty ventricle syndrome), adrenal insufficiency, beta blockade, angiotensin-converting enzyme therapy, and initial misdiagnosis.[44]

Other Reactions

Although contact reactions can occur after touching a food allergen, severe reactions are uncommon unless the antigen is ingested or absorbed through the mucosa.[10] Local pruritus, redness, or urticaria can occur in contact reactions. Isolated respiratory symptoms are uncommon during a food-induced allergic reaction, but wheezing can be part of the larger reaction.[10] Chronic asthma symptoms are unlikely to be caused by food allergy. Inhalation reactions can occur particularly if the food protein is airborne; for example, during the process of roasting nuts, steaming fish/shellfish, or boiling milk.[45,46] The smell of food alone, even a strong smell like peanut butter, is comprised of aromatic chemicals that are not proteins and would not be expected to cause an allergic reaction.[47]


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