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Is It a Food Allergy or a Food Intolerance?

Updated: Mar 7, 2022

Food allergies and food intolerances are commonly confused, as physical reactions to food intolerances occasionally resemble symptoms of food allergies. However, a food intolerance does not involve the immune system, and its symptoms are often limited to digestive problems. While they are generally less serious, an allergic food reaction can be severe or life-threatening in some cases.

How exactly can you tell the difference between a food allergy and food intolerance?

Food allergies can be triggered by even a small amount of food, and a reaction occurs every time the food is consumed. Food intolerances, however, are often dose related and symptoms are only experienced when a personal threshold for that particular food chemical is reached. This means that a person needs to eat a large portion of the food or eat the food frequently to have the symptoms if they are intolerant. For example, a person with lactose intolerance may be able to drink milk in coffee or a single glass of milk, but becomes sick if he or she drinks several glasses of milk.

All this said, here are the medical definitions of food allergy and food intolerance, and a quick outline of some potential causes of food allergies and intolerances.

What is a food allergy?

A food allergy is an unusual immune system reaction that occurs soon after eating specific foods.

If you have a true allergic reaction to food, it can affect numerous organs and various sites on the body.

The symptoms of food allergy:

The most common food allergy signs and symptoms, often called anaphylaxis, include:

  • Itchy, watery or swollen eyes

  • Tingling or itching in the mouth

  • Hives, itching or eczema

  • Swelling of the lips, face, tongue and throat or other parts of the body

  • Wheezing, nasal congestion or trouble breathing, more common in children than adults

  • Abdominal pain, diarrhea, nausea or vomiting

  • Dizziness, lightheadedness or fainting

Causes of food allergy:

Food allergies happen when the immune system – the body's defense against infection – mistakenly treats proteins found in food as a threat.

As a result, when the person eats the same food again, the antibodies are ready, so the immune system reacts immediately by releasing histamine and other chemical substances into the bloodstream. It's these chemicals that cause the symptoms of an allergic reaction.

Histamine causes blood vessels to expand and the skin to become inflamed or swollen. It also affects the nerves, making the skin feel itchy. The nose may produce more mucus, resulting in itching, burning, and a streaming nose.

Almost any food can cause an allergic reaction, but there are certain foods that are responsible for the most common food allergies.

Foods that most commonly cause allergic reactions are:

  • milk

  • eggs

  • peanuts

  • tree nuts

  • fish

  • shellfish

  • some fruit and vegetables

What is a food intolerance?

A food intolerance is characterized by difficulty digesting certain foods accompanied with an unpleasant physical reaction.

If you have a food intolerance, you may be able to eat small amounts of the offending food without trouble. You may also be able to prevent a reaction. For example, if you have lactose intolerance, you may be able to drink lactose-free milk or take lactase enzyme pills (Lactaid) to aid digestion.

The symptoms of food intolerance:

  • Nausea

  • Stomach pain

  • Gas, cramps or bloating

  • Vomiting

  • Heartburn

  • Diarrhea

  • Headaches

  • Irritability or nervousness

Causes of food intolerance include:

  • Absence of an enzyme needed to fully digest a food. Lactose intolerance is a common example.

  • Irritable bowel syndrome. This chronic condition can cause cramping, constipation and diarrhea.

  • Sensitivity to food additives. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people.

  • Recurring stress or psychological factors. Sometimes the mere thought of a food may make you sick. The reason for this is not fully understood.

  • Celiac disease. Celiac disease has some features of a true food allergy because it involves the immune system. Symptoms often include gastrointestinal issues as well as those unrelated to the digestive system, such as joint pain and headaches. However, people with Celiac disease are not at risk of anaphylaxis. This chronic digestive condition is triggered by eating gluten, a protein found in wheat and other grains.

When to see a doctor

If you think you or your child may have a food allergy, it's very important to ask for a professional diagnosis from your primary care physician or pediatrician. They can refer you to an allergy clinic if necessary.

Many parents mistakenly assume their child has a food allergy when their symptoms are actually caused by a completely different condition.

Commercial allergy testing kits are available but using them isn't recommended, as many kits are based on unsound scientific principles. Even if they are reliable, you should share the results with a health professional to seek their evaluation.

FirstMed provides lactose and other food sensitivity testing. Contact us for more information.


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