People commonly have reactions to foods. Most of the time it’s an intolerance, not an allergy, but how can you tell? Read on to learn the differences between a food allergy and food intolerance, how to tell which you’re experiencing, and what to do about it.

What is a food allergy?

Our immune systems are generally pretty good at differentiating between dangerous invaders (bacteria, viruses, etc.) and harmless substances (pollen, peanuts, etc.). The process sometimes fails, resulting in a food allergy.

Food allergies happen when the body’s immune system mistakes the protein in a food for a dangerous germ, and attacks it. This causes large amounts of immunoglobulin E (IgE) to be released. That leads to the release of histamines and other chemicals, which triggers allergy symptoms.

The body’s immune system makes IgE antibodies specific to a food allergen during the first exposure to it. Any time that food is eaten in the future, IgE antibodies bind to it. This triggers the immune system to launch a response. The process happens more quickly and aggressively each time the allergenic food is eaten.

Food allergies occur in about 4% of adults and 5% of children, according to the National Institute of Allergy and Infectious Diseases. They often appear in childhood, but can develop at any age. Food allergies can even cause a reaction to a food previously eaten with no problems.

Symptoms of a food allergy can range from mild to severe. Common symptoms include vomiting, stomach cramps, hives, wheezing, coughing, shortness of breath, swelling of the tongue, and anaphylaxis, among others.

Food allergies can’t be cured. No medications can prevent a food allergy reaction. Avoiding the food trigger is the only way to avoid a reaction.

Common food allergens

There are 8 types of foods that cause about 90% of allergic reactions. These are:

  • Wheat
  • Milk
  • Egg
  • Soy
  • Tree nuts (almonds, walnuts, cashews, hazelnuts, Brazil nuts, pistachios)
  • Peanuts
  • Fish
  • Shellfish (shrimp, lobster, crab, mussels)

It’s rare to be allergic to foods other than the common ones listed above, but it is possible. Other potential food allergens include meat, corn, gelatin, seeds (like sunflower, poppy, and sesame), spices (like garlic, mustard, and coriander), and fruits and vegetables.

What is a food intolerance?

A food intolerance is a reaction to a food that does not involve the immune system. It’s sometimes called a non-IgE mediated food hypersensitivity.

This adverse reaction to a food usually takes place within the gastrointestinal (GI) tract. The reaction may happen because the body has limited ability to digest a food. Or it could be because bacteria in the intestines digest the food and create by-products that affect the person. There may even be non-IgE mediated immune involvement in some people.

Causes of food intolerance include:

  • Missing an enzyme needed to digest a food. Lactose intolerance is an example of this as people may be missing or not have enough of the enzyme lactase.
  • Having IBS (irritable bowel syndrome) or SIBO (small intestinal bacterial overgrowth).
  • Non-IgE immune involvement
  • Being sensitive to an additive in the food.

Common food intolerances

The most common food intolerances are to these types of foods:

  • Dairy products
  • Wheat & other grains
  • Beans & legumes
  • Foods that are high in FODMAP content (fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols)

What makes food allergies and intolerances different?

The symptoms of food allergies show up more quickly than those of food intolerances. A food allergy reaction happens immediately, within 1-2 hours of eating the food allergen. A food intolerance reaction can range from immediate to 48 hours later.

Small quantities of a food allergen, even microscopic amounts, can cause reactions. Tiny amounts will generally have little to no effect on food intolerances, but a typical portion size will.

Food allergies and intolerances have some symptoms that overlap, but many that are different. Mild food allergy reactions will cause hives, redness of the skin particularly around the eyes and mouth, itchy mouth or ear canal, nasal congestion or a runny nose, or a slight dry cough among other things. A more severe food allergy reaction will cause trouble swallowing, shortness of breath, turning blue, drop in blood pressure, or a sense of impending doom. A food intolerance will cause stomach pain, bloating, gas, or brain fog among other things.

A food allergy will produce a reaction every time an allergic person eats that food. A person with a food intolerance will sometimes be able to eat a certain amount of a food while other times they’ll have a reaction for seemingly no reason.

chart of differences between food allergies and food intolerances

How can you know whether you have a food allergy vs food intolerance?

Keeping a journal of what you ate and what you experienced afterwards can be helpful. If your reaction doesn’t happen immediately and consistently every time you eat the food, then it’s not an allergy. It’s also not an allergy if you can get away with eating small amounts of the food without having a reaction. To confirm the diagnosis of a suspected food allergy, a doctor might do a blood/skin prick test or an oral food challenge.

There are tests for food intolerances, but their validity is uncertain. This means you may have expensive but useless results. An elimination diet followed by a re-introduction of the food is currently the best way to confirm a suspected intolerance.

Does it matter whether you have a food allergy vs food intolerance?

People with food allergies will react to even trace amounts of the food, so they must avoid cross-contamination. People will food intolerances can usually tolerate small amounts of the food, so they don’t have to be as strict with food preparation.

When people with intolerances tell their restaurant server that they have an “allergy” but don’t order in a manner totally consistent with that (e.g., get a gluten free bun for their burger but also order a beer), the wait staff might start to take food allergies less seriously. This can lead them being more careless about preventing cross-contamination, which can be life-or-death problematic for people with food allergies. Of course, this isn’t an issue if the word “allergy” isn’t used.

Otherwise, treatment for both a food allergy and a food intolerance often involves avoiding the offending food.

Treatment for food allergy vs food intolerance 

The only treatment for a food allergy is complete avoidance of the food. People who know they are allergic to foods may be given a prescription for injectable epinephrine, a medication that neutralizes the allergic reaction if they accidently are exposed.

The treatment for food intolerance depends on the cause of the food tolerance. If the problem is an enzyme deficiency, a replacement enzyme can be taken in the form of a pill. Lactase, the enzyme that breaks down lactose, is an example of this. Alpha-galactosidase, the enzyme that breaks down a bond commonly found in beans, lentils, and some vegetables, is another example.

If the intolerance isn’t linked to a missing enzyme, then the only option is to limit how much of the problem food is eaten. In general, someone with a food intolerance won’t need to worry about trace amounts of the food (like cross-contamination or an ingredient used in a tiny amount). They may even be able to tolerate a full-sized serving of the trigger food if they don’t have other problematic foods within the same day. Or, they may choose to indulge in the food and suffer the consequences without permanent harm.

The Bottom Line

Food allergies and food intolerances are two separate things. Food allergies involve the immune system, while food intolerances are related to something happening within the GI tract. Both can make you feel bad and seem burdensome, but only food allergies can be deadly.

To figure out which you have, monitor your reaction to the food. A reaction immediately after eating the offending food every time you eat it is likely to be a food allergy. Food intolerance tends to yield more inconsistent reactions, but the reactions generally get worse as more of the problematic food is eaten.

The symptoms of both food allergy and intolerance overlap, but there are some symptoms unique to each. People with a food allergy will need to avoid their allergenic food at all costs, but those with a food intolerance don’t need to worry about trace amounts of their problem food.



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