Food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions.
A protein in the food is the most common allergic component. These kinds of allergies occur when the body's immune system mistakenly identifies a protein as harmful. Some proteins or fragments of proteins are resistant to digestion and those that are not broken down in the digestive process are tagged by the Immunoglobulin E (IgE). These tags fool the immune system into thinking that the protein is harmful. The immune system, thinking the organism (the individual) is under attack, triggers an allergic reaction. These reactions can range from mild to severe. Allergic responses include dermatitis, gastrointestinal and respiratory distress, including such life-threatening anaphylactic responses as biphasic anaphylaxis and vasodilation; these require immediate emergency intervention. Non-food protein allergies include latex sensitivity. Individuals with protein allergies commonly avoid contact with the problematic protein. Some medications may prevent, minimize or treat protein allergy reactions.
Treatment consists of either immunotherapy (desensitisation) or avoidance, in which the allergic person avoids all forms of contact with the food to which they are allergic. Areas of research include anti-IgE antibody (omalizumab, or Xolair) and specific oral tolerance induction (SOTI), which have shown some promise for treatment of certain food allergies. People diagnosed with a food allergy may carry an injectable form of epinephrine such as an EpiPen or Twinject, wear some form of medical alert jewelry, or develop an emergency action plan, in accordance with their doctor.
Classification
Food allergy is thought to develop more easily in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma. The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.
Conditions caused by food allergies are classified into 3 groups according to the mechanism of the allergic response:
1. IgE-mediated (classic):
Type-I immediate hypersensitivity reaction (symptoms described above)
Oral allergy syndrome
2. IgE and/or non-IgE-mediated:
Allergic eosinophilic esophagitis
Allergic eosinophilic gastritis
Allergic eosinophilic gastroenteritis
3. Non-IgE mediated:
Food protein-induced Enterocolitis syndrome (FPIES)
Food protein proctocolitis/proctitis
Food protein-induced enteropathy. An important example is Celiac disease, which is an adverse immune response to the protein gluten.
Milk-soy protein intolerance (MSPI) is a non-medical term used to describe a non-IgE mediated allergic response to milk and/or soy protein during infancy and early childhood. Symptoms of MSPI are usually attributable to food protein proctocolitis or FPIES.
Heiner syndrome — lung disease due to formation of milk protein/IgG antibody immune complexes (milk precipitins) in the blood stream after it is absorbed from the GI tract. The lung disease commonly causes bleeding into the lungs and results in pulmonary hemosiderosis.
food allergy pharmacologic toxins intolerance
adverse immune response to a food protein caffeine tremors, cheese/wine (tyramine) migraine, scombroid (histamine) fish poisoning bacterial food poisoning, staphylotoxin lactose intolerance (lactase deficiency)
The reaction may progress to anaphylactic shock: A systemic reaction involving several different bodily systems including hypotension (low blood pressure),loss of consciousness, and possibly death. Allergens most frequently associated with this type of reaction are peanuts, nuts, milk, egg, and seafood, though many food allergens have been reported as triggers for anaphylaxis.
Signs and symptoms
Classic immunoglobulin-E (IgE)-mediated food allergies are classified as type-I immediate Hypersensitivity reaction. These allergic reactions have an acute onset (from seconds to one hour) and may include:
Symptoms of allergies vary from person to person. The amount of food needed to trigger a reaction also varies from person to person. Symptoms vary depending on the severity of the allergy, and they can appear in as little as a few minutes or may take up to an hour. Symptoms affect the skin, gastrointestinal tract, and in severe cases, the respiratory tract and blood circulation.
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