Difference between Food Allergy and Food Intolerance

A food allergy is a serious and sometimes life-threatening reaction to a component of a food that involves the immune system (a network of cell types that work together to defend and protect the body from viruses, infections and disease). When exposed to the allergen, the person’s immune system over-reacts, resulting in the reaction.

Allergens are Related to Protein Sequences

Allergens in foods are composed of a particular sequence of amino acids that make up the protein part of that food.

If you think of proteins as a train, the amino acids are the individual ‘cars’. The ‘cars’ can be in different orders. Say you have only five ‘cars’ in a train (a,b,c,d and e) they could be ordered a,b,c,d,e or a,c,b,e,d or a,d,e,b,c etc. An allergy is when your body overreacts to a very particular amino acid sequence in that protein (e.g. a,d,e,b,c). Whenever your immune system sees that amino acid sequence in any food, it will respond as if it were being attacked and launch an immune-system response.

In long protein chains, the particular sequence that causes the immune reaction may appear somewhere within many other amino acid sequences that do not.

Food Intolerance

Often time, people say they are ‘allergic’ to a food because it makes them feel unwell when they eat it, but they may actually be ‘intolerant’ to it, rather than actually allergic. Some of the symptoms of food intolerance and food allergy are similar, but the difference between the food intolerance and food allergy is important. If you are allergic to a food, the allergen triggers a response of the immune system.

Food Protein-Induced Enterocolitis Syndrome (FPIES)

Food Protein-Induced Enterocolitis Syndrome is a serious type of food allergy triggered by eating or drinking a food allergen and which results in vomiting and diarrhea.

Food Protein-Induced Enterocolitis Syndrome often develops in babies, usually when they are introduced to solid food or formula containing the food. In some cases, symptoms can be severe enough to cause dehydration and shock brought on by low blood pressure. The most common culprits include milk, soy and grains.

Antibodies or IgE-mediated Allergic Reactions

In some allergy, your immune system may produce antibodies called Immunoglobulin E (IgE) to a specific protein (amino acid sequence). These antibodies are responsible for the release of specific chemicals that result in an allergic reaction and a full-scale response of the immune system. This reaction usually causes symptoms in the nose, lungs, throat, sinuses, ears, lining of the stomach or on the skin. Each type of IgE reacts only to a specific allergen, so some people are only allergic to one food because they only have one IgE antibody to that substance. Other people may have several IgE antibodies to different foods and therefore will have an immune response to several different foods.

Allergies: Mild to Life-Threatening

Food allergy reactions can be mild like itchy skin or hives (raised red bumps on the skin) or be life-threatening, such as anaphylaxis which causes a person to be unable to breathe and go into shock (drop in blood pressure). People with this type of allergy must be very careful to avoid the food s they are allergic to, as coming into contact with even a tiny amount of the food can be trigger a life threatening immune-system reaction.

Note: If you know someone with food allergies, please click the “share” button so that others may know how serious, and even life-threatening this can be.

Cross Reactivity

Being allergic to a food (or more specifically, being allergic to a particular amino acid sequence in that food) may also result in being allergic to a similar protein found in something else. For example, if you are allergic to banana, you may also develop reactions to papaya or kiwi. This is known as cross-reactivity. Cross-reactivity occurs when the immune system recognizes an amino acid sequence (or part of that amino acid sequence) in a protein in a food from the same ‘family’ of fruit or vegetable one is allergic to.

Cross-reactivity can also occur in those with a latex allergy (which is “rubber”; the liquid found in the center of certain tropical plants) and foods such as bananas, avocados, kiwi, chestnut and papaya (which originate from trees that contain latex in their core).


Allergies may be screened for using a skin prick test. In skin testing, an Allergist (a physician with a specialty in allergy) places a small amount of an extract made from the food on the patient’s back or arm.  If a raised bump or small hive of bumps develops within 20 minutes, it indicates a possible allergy.

Those with serious or life-threatening allergens will have antibodies (IgE or IgA) to that specific protein present in their blood (e.g. IgE antibody to peanut). The presence of these antibodies can be determine by a blood test.

Many food allergies are first diagnosed in young children, though they may also appear in older children and adults. While many children outgrow a food allergy they had a young children, it is also possible for adults to develop allergies to particular foods they have been exposed to repeatedly over time, with no previous reaction.

Major Food Allergens

Eight foods are responsible for the majority of allergic reactions:

• Cow’s milk

• Eggs

• Fish

• Peanuts

• Shellfish

• Soy

• Tree nuts

• Wheat

More recently, sesame has been added to this list, as well as mustard seed.

Oral Allergy Syndrome

When people are allergic to non-foods (such as tree or grass pollen) may also react to foods that are in the same “family” as the tree or grass pollen. That is, there is a common amino acid sequence in the food as in the pollen. This is known as Oral Allergy Syndrome (OAS).

For example, if you are allergic to ragweed, you may also develop reactions to bananas or melons. This reaction occurs because the proteins found in the fruit or vegetable are very similar to the protein (or more specifically the amino acid sequence) found in pollen from trees and grasses. The proteins in the food are identified by the body’s immune system and cause an allergic reaction; a response of their immune system.

The most frequent allergic reaction involves itchiness or swelling of the mouth, face, lip, tongue and throat. Symptoms usually appear immediately after eating raw fruit or vegetables, although the reaction can occur an hour or more later. In rare and very serious cases, Oral Allergy Syndrome can cause severe throat swelling or even a systemic reaction, called anaphylaxis.

If one is allergic to birch tree pollen, for example (a primary airborne allergen responsible for symptoms in the springtime) that person may have allergic reactions triggered by peach, apple, pear, kiwi, plum, coriander, fennel, parsley, celery, cherry and carrot and some tree nuts such as almond and walnut.

People with allergies to grasses (also a springtime airborne allergen) may also have a reaction to peaches, celery, tomatoes, melons (cantaloupe, watermelon and honeydew) and oranges.

Those with reactions to ragweed (a late summer and fall airborne allergen) may also have symptoms when eating foods such as banana, cucumber, melon, and zucchini.

If one has Oral Allergy Syndrome, avoid eating foods in the same family as the pollen (especially during the allergy season of the pollen) may minimize the symptoms and/or the likelihood of severe allergic reactions. Taking oral antihistamines during the specific pollen season may also reduce the risk of a severe allergic reaction.

Immediate or Delayed-Onset Anaphylaxis

The majority of people with anaphylaxis react within seconds or minutes of being exposed to the food they are allergic to (common with peanut allergy), but another form of anaphylaxis results in people not reacting for 6-8 hours after consuming the food (or a commonly a food that has inadvertently been exposed to that allergen via cross-contamination in the kitchen). This is known as “delayed onset anaphylaxis”. It is associated with the same life threatening symptoms (being unable to breath, sudden drop in blood pressure, etc); with the only difference being how much time it takes for the immune system to launch a full-scale counter attack against exposure to the allergen. Food, medications, insect stings and exposure to latex can all trigger anaphylaxis.

Advice for those with Serious Food Allergies / Anaphylaxis — and those that know them

People with anaphylactic allergies are advised to carry with them at least one Epipen (an injection of epinephrine / adrenaline that can be self-administered) in the event of exposure. Don’t be embarrassed to let other’s know what foods you are seriously allergic to and that you carry an Epipen and where it is. That wonderful looking chocolate ice-cream cake may actually be a peanut butter chocolate ice-cream cake and you may only find out too late.

Teaching others how to use your Epipen on your behalf before an allergic reaction occurs is also wise idea. There is little time when you can’t inhale or exhale for someone to read the instructions contained with the Epipen! Ask them to call 911 as soon as possible if they see you are having a serious allergic reaction. Wearing a medical alert bracelet is an important way to let others know that you have a serious food allergy and that you carry an Epipen. It “speaks” for you when you are unable to breathe. Medical necklaces are also available. I even saw one young woman with a medical alert tattoo on her wrist!

Also, if you don’t have serious food allergies but know someone that does, please ask them to show you how to use their Epipen for them. It may be obvious to them which end of the Epipen goes into theur leg, but when they aren’t breathing they can’t tell you. You need to know what to do quickly in order to intervene. Please remember to call 911 as soon as possible so that you can get the person medical attention once the Epipen has been administered.

NOTE: If you know anyone with food allergies, please click one the “share” button to let others know how serious and even life-threatening a food allergy can be and more importantly, what they can do to possibly save a life.