A food allergy is different from food intolerance, although some people may not always know how these vary. A food allergy involves an immune system response by the body, while a food intolerance does not.
A person with a food intolerance cannot digest a substance in certain foods properly, often because they have an enzyme deficiency. A food allergy does not relate to an enzyme deficiency.
The table below shows features associated with either a food allergy or an intolerance.
| Intolerance | Allergy | |
| Onset | Symptoms appear later. | Symptoms appear soon after eating the food, usually within 2 hours, but sometimes after 4–6 hours. |
| Amount | The person can eat a very small quantity of the food with no adverse reaction. | The person cannot tolerate even small amounts of the allergen or food they are allergic to. Exposure to even a tiny amount of the food will produce a severe reaction. |
| Exposure | A reaction will occur only if the person eats the specific food. | A reaction may occur if the person eats a food that someone prepares for them in an environment that contains the allergen. |
| Effect | Reactions can be severe and extremely unpleasant but are rarely life-threatening. | Severe and potentially life-threatening reactions that may include anaphylaxis (anaphylactic shock). |
| Common trigger foods |
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An immune response or an enzyme deficiency?
Food allergies and intolerances are unwanted reactions to food that some people experience, but they are not the same and happen for different reasons.
Immune response: When a person has a food allergy, their body’s immune system responds incorrectly to a substance known as an allergen.
An allergen is not necessarily a harmful substance. Doctors call them allergens because they trigger an immune system response in certain people. However, allergens do not cause an adverse effect in most people.
According to the United States
- milk
- eggs
- peanuts (groundnuts)
- Brazil nuts, walnuts, and hazelnuts (tree nuts)
- fish
- shellfish
- wheat
- soybeans
Enzyme deficiency: A food intolerance usually means that a person has an enzyme deficiency.
Enzymes are substances in the body that enable people to digest food. If a person has an enzyme deficiency, their body cannot digest certain foods properly. The problematic food depends on the enzyme that is lacking.
Food intolerance may also result from:
- certain chemicals in foods
- food poisoning due to the presence of toxins
- the natural occurrence of histamine in some foods
- the presence of salicylates that occurs in many foods
- specific food additives
Food allergies and food intolerance have different symptoms.
Allergy symptoms
According to
- hives
- itchiness
- swelling of the face, lips, and tongue
- swelling of the throat and airways, leading to breathing difficulties
- dizziness, lightheadedness, and fainting
- gastrointestinal symptoms, including vomiting and diarrhea
- a sudden drop in blood pressure
- a fast, irregular pulse
- a loss of consciousness
If swelling occurs in the airways, this can make it difficult for a person to breathe. If the airway closes, this can become fatal.
An allergic reaction can happen suddenly. If a person shows symptoms of an allergic reaction, they need medical help immediately.
Intolerance symptoms
The main symptoms of a food intolerance are:
- intestinal gas
- abdominal pain
- diarrhea
Other symptoms may occur, but the core symptoms relate to a person’s gut.
Some symptoms of food allergy and food intolerance can be similar. This makes an accurate diagnosis more difficult.
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If a person has a food allergy or an intolerance, they may have to avoid the food that appears to cause it. They may also have to check the ingredients of food products carefully, whether buying for home consumption or eating out.
In summary, prevention means:
- A person with a known allergy must avoid the trigger food. Not doing so could be dangerous. The person also should carry an epinephrine autoinjector for use in case of an emergency.
- A person with an intolerance can avoid discomfort by avoiding the trigger food, but they will not face a life-threatening situation.
Since 2004, the Food Allergy Labeling and Consumer Protection Act (FALCPA) states that all packaged foods that manufacturers produce in the U.S. must carry information in simple, clear language about the eight most common allergens.
These widespread allergens are milk, eggs, wheat, soy, peanuts, tree nuts, fish, and crustacean shellfish.
There has been concern recently that the cases of allergy and intolerance are rising.
The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH) report that around
In 2016, the Centers for Disease Control and Prevention (CDC) estimated that
However, in 2017, a study of electronic health records of more than 2.7 million people in the U.S. suggests that the percentage of the population with either an allergy or intolerance is lower than this, at 3.6 percent overall.
People may not always be aware of the difference between an allergy and an intolerance, and they may not always report an allergy or intolerance to their doctor. For these reasons, it can be difficult to establish exact figures.