What is an ‘Allergy’?


On this page I define what an allergy is and what an allergen is. It is important to note that there are many complaints and conditions that mimic allergy. You will see that ‘Allergy’ is a very specific immune response.


The term allergy is all too often used for any untoward reaction, feeling, symptom, or sign that affects us and it is sometimes used inappropriately. Allergy is a very specific hypersensitivity reaction that involves the immune system. It is a type of a hypersensitivity reaction.

There are four kinds of hypersensitivity reactions; type 1 is classic, IgE mediated allergy, type 2 is due to antibodies of different classes, IgG and IgM, that are directed against body tissue, type 3 is IgG or IgM antibodies that bind to a foreign protein in our circulation, and a type 4 reaction is mediated by cells and not antibodies.

Type          Mechanism          Example

Type 1             IgE                    Anaphylactic shock

Type 2        IgG/IgM             Autoimmune disease

Type 3        IgG/IgM            Serum sickness

Type 4         Cells                   Poison ivy

Allergy testing in the clinic looks for IgE antibody so it would be a type 1 reaction.

What causes allergy?

Allergy is caused by allergens which are materials made mostly of proteins or when something like a medication binds to a protein in the body changing its configuration. In those people prone to develop allergy, an antibody called IgE is made. This antibody binds to cells called mast cells. These are the cells that contain the mediators that cause the symptoms of allergy and they are found in the skin, in the gut, in the respiratory tract,  and around blood vessels.

IgE antibodies can be made to the following items:


Mold spores

Animal danders/saliva

Insect venom

Insect fecal particles




What are the symptoms due to allergy?

When a foreign protein enters the body, those who have an allergic response make an IgE antibody specific to that protein. The antibody directed to that protein binds to cells and those cells release mediators when there is an exposure to the foreign protein. Many of the allergic responses are exaggerated and are directed towards clearing the foreign protein from the body.

For example, if the foreign protein or allergen is a pollen and  gets into the eye-there are tears, when the allergen is in the nose-there is sneezing, when it gets into the lower realms of the respiratory tract- coughing. Consider when the allergen is a food and is eaten- there are two choices for the body to rid itself of the food by vomiting or by diarrhea.  There are of course additional manifestations of allergy that may involve the cardiovascular system (anaphylactic shock) and the skin (hives and some forms of eczema).

Matching symptoms with established allergic conditions- fit the template

The symptoms should match a template of allergic conditions and importantly there should be some notion of a cause/effect relationship for a triggering exposure.  There are a number of conditions that have been thought to be due to ‘allergy’ but through careful reviews, using evidence-based approaches, have not  proved to be allergy mediated.  These concerning conditions include autism, behavior disorders, colic, and migraine headache. I plan to go into more detail on these frustrating conditions on another page.

History, History, and more History-

The story (history) is the most important aspect of allergy. The specialty of allergy is very dependent upon  the history of the reaction and its many specifics. All too often contemporary thought is that a ‘test’ of sorts is the standard for allergy, it is not!

I will delve into allergy testing on another page but for now please note that the value of any test done for allergy is only as good as the story that supports it. The test shows that the patient is making an antibody, the clinical relevance of that antibody depends on a savvy history taking and establishment of exposure with subsequent symptoms- a good, patient, extensive history.

Conditions that may be due to allergy-

The classic allergic conditions include- Asthma, Anaphylactic shock,  Rhinitis, Hives, Eczema, and the gastrointestinal conditions Vomiting/Diarrhea.


I would recommend caution and care when considering the concept of allergy and remember these points

1. history is critical

2. the immune system is involved

3. tests make no one allergic, they support a clinical impression

4. there are certain conditions shown to be due to allergy

5. allergens have specific biochemical properties.

Just because Joey does not like to do his homework does not (necessarily) mean that he is allergic to it!

7 Responses

  1. bethanyll22 - January 8, 2009

    Can you be allergic to cigarette smoke?

  2. fleickly - January 8, 2009

    A good question and one frequently asked by families. The quick answer is ‘no’. The body does not make an allergic response to smoke. We do no make allergy type antibodies to smoke. Smoke can cause symptoms that we see in allergy such as coughing, wheezing, running nose, congestion, and sneezing. Smoke acts as an irritant to the airways causing very similar symptoms. It does not work or function like an allergen. We could not perform any skin or blood test for smoke.

  3. Seeking the best care for allergy « Allergies: A Leickly Story - February 15, 2009

    […] What is an ‘Allergy’?   […]

  4. Sue - May 1, 2009

    Do you have any air quality companies that you would recommend?

  5. fleickly - May 4, 2009

    Sue, I am not sure about your question. Air quality can mean many different things. Is your interest overall air quality or allergen related air quality. Let me know the specifics of your question.

  6. Sue - May 4, 2009

    I would like to know if there is a way to test for mold, dust mites, etc., to know if we have issues in our home and where.

  7. fleickly - May 4, 2009

    There are a number of companies that will look for mold. Be careful that the investigative company does not also offer remediation. That would be a conflict of interest. Your local country health department could help with the mold evaluation or at least have some companies in mind that they work with.
    As for house dust mites, you can almost guarantee that they will be in fiber filled items- mattress, box spring, pillows, comforters, carpet, and other furniture. The house dust mite allergen is a heavy particle and settles quickly. It is more an issue whith things we have our face close to and I need to mention that inch for inch there are more house dust mites in stuffed animals than anything else created by mankind.
    I hope this helps,