What Causes Allergies?

Frederick R. Jelovsek MD, MS

When your nose is runny and eyes are itchy you probably are just interested in relief; not in why this reaction is happening. Sometimes though, it is helpful to know the detail of how a medical condition is produced especially when it is one that is chronic and going to afflict you the rest of your life. Allergy is one such condition. People with allergies have genes that make them more likely to develop a bodily reaction to various substances they are exposed to.

The body's immune system is the main protective mechanism to maintain health. It identifies and fights off bacteria, viruses, parasites, cancer cells, food and any foreign protein substance. Lymphocytes are one type of white cell in your blood and they are a major component of the immune system. As soon as a foreign protein enters the body, the lymphocytes identify the protein, fingerprint it and determine if it belongs to this body or not. "Lymphocytes act like traveling customs agents. Everywhere they go, they are busy checking the passports of every cell they encounter. Whenever they discover a cell that seems threatening, they immediately begin countermeasures against it. The biochemical process behind these countermeasures is amazing! (1)

Causes Of Allergies

Allergies result when this immune system is hypersensitive, overreactive. When the system misidentifies harmless proteins as serious enemies and then reacts out of proportion to the threat, you get symptoms from this major bodily battle. Those symptoms may be mildly annoying or a major illness. Usually for your immune system to overreact like this you must have a genetic tendency for it.

After the lymphocyte identifies the foreign protein (antigen) it goes back to a lymph node where it changes into a different type of white blood cell (mast cell). The mast cell manufactures a chemical called an immunoglobulin that is exactly configured like a laser ray to destroy the specific protein that the lymphocyte identified in the first place. Of the different immunoglobulins (IgA, IgD, IgE, IgG, IgM), Ig E is the class that forms an allergic reaction. They attach to other white blood cells in what is called the sensitizing exposure,

When the protein comes into the body again, at least 7-10 days after the sensitizing reaction, the IgE primed mast cells release many chemicals including histamine that try to destroy the "invading" protein. Histamine lowers the local blood pressure and causes itching and swelling . It can also cause wheezing, an itchy, runny nose, nausea, vomiting or diarrhea. That is why "anti- histamine" drugs are used to treat allergies.

Specific allergies can be identified either by a blood test for IgE or by a scratch test in which the suspected allergen is "scratched" into the skin to see if the body reacts to it with redness and swelling. A problem with specific identification of allergies, however is what is called cross-reactivity. Sometimes proteins of different but similar substances, e.g., shrimp and crab meat, can both cause an allergic response even though the body had previously been exposed to only one of them. Even so, allergen identification is very important so that you can avoid the offending allergen in the first place.

Understanding Allergies

Now why is it important to know the mechanism of action for allergies? If there is a genetic disposition for your body to form allergic responses, there is not much you can do - correct? No. You basically have two practical choices for self-care. Identify the causative agents so you absolutely avoid them and treat with anti- histamines for mild but annoying allergic reactions. Fortunately there is a self home test for food allergies, Food allergy test kit, and also one that tests for grasses, molds, dust and cat allergies along with some common food allergies such as milk, eggs and wheat, MyAllergyTest. For other tests you will have to have a doctor's order and have a blood drawn and sent to a special laboratory. If you are having serious reactions, see an allergist for allergen identification and treatment.

One last tip. The gold standard for diagnosing allergies are the scratch test sets applied in the allergist's office. Many times, however, you may not want to suffer the reactions you get during testing or you may fear causing a new allergy by sensitizing through your skin to a new substance you are not already allergic to. The allergy doctor may prefer the scratch tests because they are more accurate but you can ask to have the blood test done instead, with subsequent scratch testing if needed, to narrow down the specific allergen from a general group of substances.