The Difference Between Food Allergy and Food Intolerance

While food allergies and food intolerances can cause similar symptoms, the underlying causes are different.

A child has a skin reaction to an allergen during a skin prick test. The skin prick test is one diagnostic test healthcare providers may use to diagnose food allergies.

Updated on March 11, 2024

Food allergies and food intolerances are distinct conditions that can sometimes be confused with one another. Although food allergies and food intolerances can cause similar symptoms, there are significant differences in the underlying causes, the potential complications, and how the conditions need to be managed.

What is the main difference?

The main difference between a food allergy and a food intolerance:

  • A food allergy involves an abnormal response by the immune system.
  • A food intolerance does not involve the immune system.

Food allergies and the immune system

The immune system is a network of organs, tissues, vessels, lymph nodes, white blood cells, and antibodies that protect the body from infectious agents and harmful substances, such as bacteria, viruses, and parasites. The immune system also clears away abnormal cells, such as cancerous cells and cells that are damaged by injury or infection.

The immune system works by identifying—and then attacking—things that do not belong in the body while ignoring things that do belong in the body.

When a person has a food allergy, the immune system activates when it comes into contact with certain foods or substances found in foods. Peanuts, eggs, milk, wheat, nuts, fish, and shellfish account for most food allergies (though a person can be allergic to almost any food).

Non-allergic adverse reactions to foods

A food intolerance is an adverse reaction to food that does not involve the immune system. Food intolerances can have several different causes:

Inadequate digestive enzymes

  • The body depends on specific chemicals called enzymes to digest different types of food. Sometimes a person’s digestive system will not make enough of an enzyme needed to digest a certain food.
  • One of the most well-known examples is lactose intolerance. When a person is lactose intolerant, the small intestine only produces low amounts of the enzyme lactase, which is needed to digest lactose (a sugar found in milk and other dairy foods).

Reactions to substances found in foods

  • Some people have reactions to certain substances found in foods.
  • This includes substances like caffeine (found in tea, coffee, and soda) and chemicals called salicylates, which are produced by many edible plants as a natural defense against insects and bacteria.
  • It also includes additives, like monosodium glutamate (or MSG, a naturally occurring chemical added to certain foods to enhance flavor) and sulfites (another naturally occurring chemical, commonly used as a preservative).

Irritable bowel syndrome (IBS)

  • A syndrome is a group of signs and symptoms that occur together, but do not have a clearly identifiable cause.
  • Irritable bowel syndrome (IBS) is a group of gastrointestinal symptoms—abdominal pain, cramps, gas, bloating, diarrhea, and constipation (and sometimes, alternating diarrhea and constipation).
  • People with IBS often find that certain foods trigger symptoms. These include fruits, vegetables, wheat products, dairy foods, and artificial sweeteners.
  • Another term to know is FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) which are carbohydrates found in a variety of foods in varying amounts. High FODMAP foods tend to trigger IBS symptoms more than low FODMAP foods.

Overlapping symptoms

Food allergies and non-allergic adverse reactions to foods can overlap in the symptoms that they cause:

  • Gastrointestinal symptoms are often the first symptoms to appear in infants and children who have food allergies. GI symptoms are also associated with food intolerances like lactose intolerance, as well as IBS.
  • Hives, itching, skin rash, and angioedema are associated with food allergies involving eggs, milk, peanuts, and nuts. These symptoms can also occur as a result of a reaction to food additives.
  • Anaphylaxis is a life-threatening allergic reaction that causes the body to go into shock. It is something that people with food allergies and parents of children with food allergies need to be prepared for—typically by carrying a self-injecting epinephrine syringe and having an emergency plan. Though less common, cases of anaphylaxis have also been reported with reactions to food additives.

Symptoms should always be evaluated by a healthcare provider. There are diagnostic tests that can help a healthcare provider determine if a reaction to food is allergic or non-allergic, such as the skin prick test and allergy blood test. These tests can be used to diagnose food allergies and can also rule out certain types of food allergies as a cause of symptoms.

Always consult a healthcare provider before making significant changes to a diet. Eliminating foods and food groups from a person’s diet can cause complications at any age and can impair the normal growth and development of a child. Parents of children who have food allergies will need to work closely to ensure a child’s diet is meeting nutritional needs.

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