Some foods are more likely to cause allergic reactions than others. Most people are not allergic to more than a handful of foods (AAFP 2008), but cross reactions are possible. Food allergies can cause a variety of symptoms ranging from the merely annoying to the potentially fatal.
In principle, any food can trigger an allergic response, but certain foods are more likely to trigger an allergic response than others. The top eight common food allergens, found in 90% of food allergies, are as follows (FAAN):
- Peanuts
- Tree nuts
- Cow's milk (dairy)
- Eggs
- Wheat
- Soy
- Fish
- Shellfish
Contrary to popular belief, strawberries and tomatoes are not particularly common food allergens (AAFP, 2008).
When a person is allergic to a given food, he or she is likely to be allergic to related foods. Thus a person who is allergic to one type of shellfish is more likely to react to other types of shellfish as well, a phenomenon known cross-reactivity. Allergies in the same person to unrelated foods, such as peanuts and tree nuts (which, though superficially similar, come from different botanical families) are known as coincidental allergies (AAAAI 2008).
The most common symptom of an allergic reaction caused by food is hives, red swollen bumps on the skin that are intensely itchy. Hives are transient, and as one area with hives clears up, another may break out (AAAAI 2008). Hives may occur only in parts of the body that touch the food, such as the hands, or they may occur over other parts of the skin. Another common skin symptom is eczema, also called atopic dermatitis, which results in red, scaly, itchy skin. Though by definition allergic reactions have a rapid onset, eczema may become a chronic condition in individuals with food allergies (AAAAI 2008).
Food allergies can cause a plethora of gastrointestinal symptoms when the offending food is consumed, including vomiting, diarrhea, cramps, intense itchiness of the mouth and throat, stomach swelling, and gas (AAAAI 2008).
Though asthma is often comorbid with food allergies and an allergic reaction to food may cause bronchoconstriction, foods are rarely the main cause of chronic asthma, especially in adults (NIH 1997).
A severe reaction called anaphylaxis can occur with food allergies. Anaphylaxis is life-threatening, with symptoms that can include airway constriction, loss of blood pressure, and shock, as well as swelling, itchiness, vomiting, and other symptoms. Because of the risk of anaphylaxis, allergists often prescribe portable single-use epinephrine injectors to their patients with food allergies for use in an anaphylactic emergency.