1. Signs and symptoms

2. Cause
    Sensitization  Atopy  Cross-reactivity 

3. Pathophysiology
    Acute response  Late-phase response 

4. Diagnosis
    Differential diagnosis 

5. Prevention
    Inhalation exposure 

6. Treatment
    Epinephrine  Antihistamines  Steroids 

7. Epidemiology
    United States 

8. Society and culture
    Regulation of labelling  Ingredients intentionally added  Trace amounts as a result of cross-contamination  Genetically modified food 

9. Research

10. See also

11. References

12. External links

A food allergy is an abnormal immune response to food.^[1] The symptoms of the allergic reaction may range from mild to severe.^[1] They may include itchiness, swelling of the tongue, vomiting, diarrhea, hives, trouble breathing, or low blood pressure.^[1] This typically occurs within minutes to several hours of exposure.^[1] When the symptoms are severe, it is known as anaphylaxis.^[1] A food intolerance and food poisoning are separate conditions, not due to an immune response.^[1][1]

Common foods involved include cow's milk, peanuts, eggs, shellfish, fish, tree nuts, soy, wheat, rice, and fruit.^[1][3][2] The common allergies vary depending on the country.^[1] Risk factors include a family history of allergies, vitamin D deficiency, obesity, and high levels of cleanliness.^[1][3] Allergies occur when immunoglobulin E (IgE), part of the body's immune system, binds to food molecules.^[1] A protein in the food is usually the problem.^[3] This triggers the release of inflammatory chemicals such as histamine.^[1] Diagnosis is usually based on a medical history, elimination diet, skin prick test, blood tests for food-specific IgE antibodies, or oral food challenge.^[1][3]

Early exposure to potential allergens may be protective.^[3][3] Management primarily involves avoiding the food in question and having a plan if exposure occurs.^[3] This plan may include giving adrenaline (epinephrine) and wearing medical alert jewelry.^[1] The benefits of allergen immunotherapy for food allergies is unclear, thus is not recommended as of 2015.^[4] Some types of food allergies among children resolve with age, including that to milk, eggs, and soy; while others such as to nuts and shellfish typically do not.^[3]

In the developed world, about 4% to 8% of people have at least one food allergy.^[5][6] They are more common in children than adults and appear to be increasing in frequency.^[6] Male children appear to be more commonly affected than females.^[6] Some allergies more commonly develop early in life, while others typically develop in later life.^[5] In developed countries, a large proportion of people believe they have food allergies when they actually do not have them.^[7][8][9] The declaration of the presence of trace amounts of allergens in foods is mandatory only in Brazil.^[49][50][10]

Signs and symptoms

Food allergies usually have a fast onset (from seconds to one hour) and may include:^[11]

• Rash
• Hives^[11]
• Itching of mouth, lips, tongue, throat, eyes, skin, or other areas^[11]
• Swelling (angioedema) of lips, tongue, eyelids, or the whole face^[11]
• Difficulty swallowing^[11]
• Runny or congested nose^[11]
• Hoarse voice^[11]
• Wheezing and/or shortness of breath^[11]
• Diarrhea, abdominal pain, and/or stomach cramps^[11]
• Lightheadedness^[11]
• Fainting^[11]
• Nausea^[11]
• Vomiting^[11]

In some cases, however, onset of symptoms may be delayed for hours.^[11]

Symptoms can vary. The amount of food needed to trigger a reaction also varies.^[12]

Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated through wheezing and cyanosis. Poor blood circulation leads to a weak pulse, pale skin and fainting.^[13]

A severe case of an allergic reaction, caused by symptoms affecting the respiratory tract and blood circulation, is called anaphylaxis. When symptoms are related to a drop in blood pressure, the person is said to be in anaphylactic shock. Anaphylaxis occurs when IgE antibodies are involved, and areas of the body that are not in direct contact with the food become affected and show symptoms.^[14] Those with asthma or an allergy to peanuts, tree nuts, or seafood are at greater risk for anaphylaxis.^[15]

Cause

Although sensitivity levels vary by country, the most common food allergies are allergies to milk, eggs, peanuts, tree nuts, seafood, shellfish, soy, and wheat.^[16] These are often referred to as "the big eight".^[17] Allergies to seeds — especially sesame — seem to be increasing in many countries.^[18] An example an allergy more common to a particular region is that to rice in East Asia where it forms a large part of the diet.^[19]

One of the most common food allergies is a sensitivity to peanuts, a member of the bean family. Peanut allergies may be severe, but children with peanut allergies sometimes outgrow them.^[20] Tree nuts, including cashews, Brazil nuts, hazelnuts, macadamia nuts, pecans, pistachios, pine nuts, coconuts, and walnuts, are also common allergens. Sufferers may be sensitive to one particular tree nut or to many different ones.^[21] Also, seeds, including sesame seeds and poppy seeds, contain oils where protein is present, which may elicit an allergic reaction.^[21]

Egg allergies affect about one in 50 children but are frequently outgrown by children when they reach age five.^[22] Typically, the sensitivity is to proteins in the white, rather than the yolk.^[21]

Milk from cows, goats, or sheep is another common food allergen, and many sufferers are also unable to tolerate dairy products such as cheese. A small portion of children with a milk allergy, roughly 10%, have a reaction to beef. Beef contains a small amount of protein that is also present in cow's milk.^[23]

Seafood is one of the most common sources of food allergens; people may be allergic to proteins found in fish, crustaceans, or shellfish.^[24]

Other foods containing allergenic proteins include soy, wheat, fruits, vegetables, maize, spices, synthetic and natural colors,{{citation needed|reason=colors rarely contain protein|date=November 2016}} and chemical additives.

Sensitization

Sensitization can occur through the gastrointestinal tract, respiratory tract and possibly the skin.^[28] Damage to the skin in conditions such as eczema has been proposed as a risk factor for sensitization.^[29] An Institute of Medicine report says that food proteins contained in vaccines, such as gelatin, milk, or egg can cause sensitization (development of allergy) in vaccine recipients, to those food items.^[30]

Atopy

Food allergies develop more easily in people with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema, and asthma.^[31] The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.{{mcn|date=November 2014}}

Cross-reactivity

Some children who are allergic to cow's milk protein also show a cross-sensitivity to soy-based products.^[32] Some infant formulas have their milk and soy proteins hydrolyzed, so when taken by infants, their immune systems do not recognize the allergen and they can safely consume the product. Hypoallergenic infant formulas can be based on proteins partially predigested to a less antigenic form. Other formulas, based on free amino acids, are the least antigenic and provide complete nutritional support in severe forms of milk allergy.

People with latex allergy often also develop allergies to bananas, kiwifruit, avocados, and some other foods.^[33]

Pathophysiology