Food allergies vs. food intolerances: What’s the difference?

People have issues with food. Some have allergies, some have intolerances, and some people just really don’t like peanuts. But without proper diagnosis, things can get muddled. So, in honor of Food Allergy Awareness Week, here’s a crash course in food allergies and intolerances, and how they’re different. For definitions of specific terms, check out the bottom of this post.

So, what goes on during a true allergic reaction?

The element that separates a true allergic reaction from other food-related disorders is an immune response, specifically two elements – the production of massive amounts of immunoglobulin E (IgE), an antibody in the blood, and the activation of mast cells. These cells are common in areas of the body that are typical sites for an allergic reaction, including the lungs, skin, eyelids, nose and throat. Mast cells assist in allergic reactions by releasing substances such as histamine and heparin.

But what in the food actually causes the reaction? The answer is proteins that are specific to each allergenic food. Some of these proteins cannot be broken down by heat from cooking or by digestive acids or enzymes. Since they can’t be destroyed, the proteins cross the gastrointestinal lining, enter the bloodstream, and cause allergic reactions.

Once an allergenic food is digested, it triggers the production of large amounts of IgE specific to the food item. The IgE then attaches to the surface of mast cells the first time the food is eaten. When the person eats the food anytime after the first ingestion, it interacts with the IgE attached to the mast cells, causing the cells to release chemicals such as histamine to mediate the reaction. Depending on where the chemicals are released, a person will feel different symptoms. For example, if they’re released in the ears, nose or throat, the person may feel itching in their mouth and could experience swelling. Severe reactions in the nose and throat are called anaphylaxis, which is life threatening. Other symptoms of a reaction include hives (if the mast cells in the skin release chemicals) or abdominal pain and diarrhea (if the mast cells in the gastrointestinal tract release chemicals).

How much allergenic protein does it take to trigger a reaction?

Research is ongoing but according to available data, it’s not possible to set a limit of allergenic protein that covers everyone as people have different thresholds for reactions.

How fast does an allergic reaction happen?

It really depends on digestion. Allergic reactions stemming from foods may start with itching in the mouth, even as the food is being chewed. As it’s digested, abdominal symptoms such as vomiting may begin. As the allergens cross the gastrointestinal lining and into the blood stream, they can cause a drop in blood pressure. Symptoms can begin only a few seconds after ingestion.

OK, so that’s an allergy. What is intolerance?

The biggest difference between a food allergy and intolerance is easy to remember: a food allergy has an immune response while intolerance does not. For example, lactose intolerance (intolerance to a sugar called lactose in milk and dairy products) mimics some of the symptoms of food allergies. However, lactose intolerance is caused by a lactase enzyme deficiency, that is, a person’s body doesn’t have enough of the proper enzyme to digest lactose rather than an immunological response to lactose.

Other intolerances include celiac disease, also known as gluten intolerance. Gluten is a protein found in many common foods including wheat, rye and barley. Celiac disease affects 1 in 133 people in the U.S., according to

Those with celiac disease suffer a flattening of the villi in the intestine, which makes it difficult for them to absorb nutrients, according to the Celiac Disease Foundation.

May also marks Celiac Disease Awareness Month.

How do I know what’s wrong?

Only a physician can diagnose an allergy versus intolerance.

The allergy glossary

Allergenic: Something that can cause an allergic response.

Anaphylaxis: A type of allergic reaction that affects the entire body and can be life-threatening. Symptoms occur within minutes (and can be as quick as a few seconds) after exposure to the allergen and include abdominal pain, difficulty breathing, slurred speech, anxiety and confusion, hives, skin discoloration, fainting, diarrhea, and nausea. Anaphylaxis requires an immediate, professional medical response.

Heparin: A chemical especially present in the lungs and liver that acts as a blood thinner and reduces the clotting time of blood.

Histamine: A chemical released during allergic reactions that mediates inflammation. It causes dilation of blood vessels, muscle contraction and triggers the release of gastric acid.

Immunoglobulin E: An antibody in the blood that plays a key role in allergic reactions.

Mast cell: A tissue cell that is part of the immune system that mediates inflammatory responses such as allergic reactions.

For previous blog posts about Food Allergy Awareness Week, click here and here.

For Neogen’s Food Allergy Handbook, click here.

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