Food Allergy & Food Intolerance – Features, Symptoms, and Treatment

A food allergy is different from food intolerance. A food allergy involves an immune system response, while food intolerance does not.

A person with a food intolerance cannot properly digest a substance in certain foods, often because they have an enzyme deficiency. A food allergy is not related to an enzyme deficiency.

Features of food allergy and intolerance

Below are some features associated with either a food allergy or an intolerance.

The onset of symptoms is different.

Food allergy symptoms appear soon after eating the food

Food intolerance symptoms appear later.

The amount of food consumed is different.

If an individual has a food allergy, they cannot tolerate even small amounts of the allergen, or food that they are allergic to. If someone with a peanut allergy is exposed to even a tiny amount of peanut, they may have a severe reaction.

Someone with a food intolerance can eat a very small quantity of the food with no adverse reaction.

A person with a food allergy may have a reaction even if the food was prepared in an environment which contained the allergen, or if they enter a place where the allergen is present.

An immune response versus or an enzyme deficiency?

In a food allergy, a protein causes an allergic reaction, known as an immune response. An “allergen” is a protein that causes a food allergy.

Allergens themselves are not harmful substances. Most people can be exposed to them without any adverse effects. They are called allergens because they affect some people by triggering a response in their immune system.

A food intolerance usually means that the person has an enzyme deficiency, so that their bodies cannot digest the food properly.

Food intolerance may also be caused by certain chemicals in foods, by food poisoning due to the presence of toxins, by the natural occurrence of histamine in some foods, by salicylates which are present in many foods, and by food additives.

Food allergies can be life-threatening.

A food allergy can sometimes lead to a severe and life-threatening allergic reaction to certain foods, known as anaphylaxis, or anaphylactic shock.

Food intolerance can cause adverse reactions that are severe and extremely unpleasant, but they are rarely life-threatening.

Symptoms of food allergy and food intolerance

Food allergy and food intolerance have different symptoms.

According to the American Academy of Allergy, Asthma, & Immunology (AAAAI), an allergic reaction to food will often cause skin problems, such as hives, itchiness, or swelling. If there are skin problems, there may also be respiratory symptoms. Gastrointestinal symptoms may include vomiting and diarrhea.

The main symptoms associated with food intolerance are intestinal gas, abdominal pain, or diarrhea. Other symptoms may occur, but the core symptoms are related to the gut.

Some symptoms of food allergy and food intolerance are similar. This makes an accurate diagnosis more difficult.

Common foods that cause allergies and intolerance

The most common foods that cause allergic reactions are:



Groundnuts, or peanuts


Nuts from trees, such as Brazil nuts, walnuts, almonds, and hazelnuts



The most common foods that cause intolerance are:



Citrus fruit

Grains that contain gluten

Milk, or lactose

Processed meats.

Treatment of a food intolerance or a food allergy

If a person has a food allergy or an intolerance, they should avoid that food, and carefully check ingredients of food products, whether for home consumption or when eating out. However, the treatment for a person who has consumes the item is different whether it is an allergy or an intolerance.

Food allergy

Since 2004, the Food Allergy Labeling and Consumer Protection Act (FALCPA) has meant that all packaged foods produced in the U.S. must carry information in simple, clear language about the eight most common allergens. These are milk, egg, wheat, soy, peanut, tree nut, fish and crustacean shellfish.

A person with a known allergy should carry an injector, such as an EpiPen, which can administer epinephrine, or adrenaline, in case of a severe reaction. They should carry two doses.

Anaphylaxis can range in severity from mild to life-threatening, and it can happen quickly. The symptoms include skin reactions, swelling, difficulty breathing, and a sudden drop in blood pressure. It is a medical emergency. A person who has an allergy may have a mild reaction on one occasion, and a severe reaction on another occasion. About 20 percent of people with an allergy have a severe reaction.

Food intolerance

Management of a food intolerance usually starts with an exclusion diet, in which the person avoids the foods suspected of causing the problem for some time, usually between 2 and 6 weeks. The patient may keep a food diary to note whether symptoms improve. After this, food is reintroduced, and reactions are noted. This can reveal which food is causing the problem.

Sometimes, the food is reintroduced without any reaction occurring. It may be that the person has developed a tolerance, or that a small amount of the food does not cause a problem.

Food intolerance varies widely between individuals, so each case is likely to be different.

Sometimes, an underlying problem makes the intolerance worse, so this should be treated appropriately.

How common are food intolerance and food allergy?

The Cleveland Clinic note that about 7 percent of children and 1 percent of adults have a food allergy. This means that most childhood food allergies eventually go away. It is estimated that approximately 10 percent of Americans are lactose intolerant.

The National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health (NIH) reports that around 1 in 20 children under the age of 5 and almost 1 in 25 adults have a food allergy.

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