What Happens During an Allergic Reaction to Food

In November 2022, the US Federal Drug Administration updated its guidelines for Edition 5 of the questions and answers regarding food allergies. This guidance was originally enacted in 1938 and required food labels to declare each ingredient by its common name except for spices, flavorings, and noncertified colors. The problem has always been that food names may not always be recognized.

Key takeaways:
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    Food allergies are immunologically mediated and can occur to any food protein.
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    Food avoidance may not be enough. Careful attention should be taken to avoid cross-contamination and cross-reactivity.
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    Those with known food allergies should have an emergency medical plan, including an allergy alert bracelet and access to epinephrine or other medications such as inhalers.

Updates are necessary to warn people of significant public health concerns. Food allergies can be mild, but they can also be severe enough to warrant medical attention and threaten lives. Labeling has had to adapt to newer products with new biotechnology and designations such as gluten-free.

The point is that food allergies affect millions of people and things are always changing. There is no cure for food allergies and avoidance is the main preventative treatment. The major food allergens are milk, eggs, fish, Crustacean shellfish, tree nuts, peanuts, wheat, and soybeans. About 20 years ago, sesame was added to the list.

It is important to understand how food allergies work. Food allergies are immunologically mediated and can occur to not just the nine food proteins above, but to any food protein.

What happens medically during a reaction to a food allergy?

Remarkably, more people don’t have food allergies. Our digestive system, particularly our intestines, encounters billions of possible antigens, or foreign substances every day. Our immunologic defense is robust, but it is also finely tuned to maintain an equilibrium called homeostasis, so we are protected and at the same time, don't react negatively to everything we eat.

It is uncommon for us to have an allergic reaction to non-protein food additives. This is fortunate, as trying figure out an allergy that is non-protein may be particularly elusive since it does not follow known immunologic pathways.

Noninflammatory immune responses that occur to ingested foods is called oral tolerance. It seems adverse reactions may be due to both environmental and genetic factors.

Most food allergies are immunoglobulin E (IgE) antibody-mediated responses. IgE works through activation by binding to special receptors in our blood called Fc receptors FcεRI and FcεRII/CD23.4 The IgE antibodies react to specific parts of the protein that the person is allergic to, called epitopes. The IgE antibodies bind to specialized cells of our immune system called basophils and tissue mast cells that are present in many areas of the body, particularly the skin, gastrointestinal tract, and respiratory system.

When the food allergy activates, there is intracellular signaling that occurs, which begins the release of inflammatory mediators such as histamine and the synthesis of other factors called chemotactic factors and cytokines, all of which produce the allergic response.

The result of this processes creates the signs and symptoms of the food allergy. These include vasodilation (skin redness), smooth muscle contraction (e.g., stomach cramping), and mucus secretion (runny or stuff nose), or other symptoms.

It is possible to have sensitization or food allergy without the development of an immunoglobulin E immune response. A notable example is an allergic response to raw fruits and vegetables in some people. There are proteins in fruits and vegetables that are shared with pollen. Examples include green peas, artichokes, sweet corn, avocado, and others. The person initially has the allergic response through breathing in the pollen or by skin exposure but can later develop an allergic food response through ingestion of the fruit or vegetable.

Lastly, there are food allergies that can be elicited through cell-mediated responses. This occurs mostly in delayed or chronic symptoms. These include disorders such as food protein-induced enterocolitis syndrome which is mediated by T cells. Other examples include those individuals who have atopic dermatitis (skin rash) from milk ingestion or an immune response to gluten proteins in grains called celiac disease.

What should you watch for if you have food allergies?

Most people recognize the need to avoid certain foods, but there are certain instances where that is impossible such as at restaurants, buffets, and picnics. There is the issue of cross-contamination and cross-reactivity with unsafe foods.

Skin contact and inhalation exposure should be considered, particularly if foods are being steamed or fried. Common food allergy occurrences are to frying fish or boiling milk. Also, it is possible to have food allergies to certain medications and cosmetics.

Cross-reactivity can occur in the following instances:

  • Eggs and chicken (< 5% of patients have both allergies).
  • Cow milk and beef (10% of patients with milk allergy react to beef).
  • Cow milk and goat milk (>90% allergic to cow milk also react to goat/sheep milk).
  • Fish (>50% allergic to any finned fish are reactive to all types).
  • Peanuts and other legumes (< 10% with a peanut allergy react to other legumes).
  • Soy and other legumes (< 5% with a soy allergy react to other legumes).
  • Wheat and other grains (25% with a wheat allergy react to rye and barley).
  • Tree nuts and other nuts (>50% with an allergy to a tree nut react to others).

Probably the most important contingency beyond avoidance is to have an emergency plan. Most patients should have this written in case of emergency, with copies available.

Many public places have emergency equipment available for food allergies such as injectable epinephrine for the initial management of anaphylaxis. Some people are advised to carry self-injectable epinephrine which can be obtained by prescription, such as EpiPen, EpiPen Jr, Adrenaclick 0.15 mg, Adrenaclick 0.3 mg, Auvi-Q 0.15 mg, Auvi-Q 0.3 mg. Be careful to store these medications properly, avoid temperature extremes, and watch the expiration dates.

Food allergies can cause discomfort or be life threatening. Consult your healthcare provider to narrow down which foods you react to, and to set up a medical emergency plan in the event you cannot avoid eating something you are allergic to.

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