An allergy is an acquired sensitivity of the immune system. This means that the body’s immune system has become sensitive to one or more common, harmless substances in our environment, such as pollen, dust, molds or even food. This sensitivity causes an immune response, which results in symptoms that range from mild (runny nose, watery eyes, sneezing and itching) or severe (hives, trouble breathing, or anaphylactic shock). Symptoms usually occur with each exposure to the allergen.

An allergen is a general term used to describe something that causes an allergic reaction. Allergens are actually tiny proteins found on certain substances. Some examples are airborne allergens, like pollen and mold; foods like shellfish, peanuts and milk. Venom from an insect sting contains allergens as do plants, like poison ivy. Allergens also exist in households, like dust mites. Only those who are prone to acquired sensitivity are regularly affected by these allergens.

Pathway of an Allergic Reaction
Two phases exist in allergic reactions, primary exposure and re-exposure. In this example the primary exposure is from allergens in the venom of an insect sting.

Anaphylaxis: An Allergic Emergency
Anaphylaxis is a life-threatening reaction. The onset of this reaction occurs within seconds or minutes of exposure. Symptoms include red raised blotches over most of the body, skin becomes warm to the touch, intense tightening and swelling of the airway makes breathing difficult, and there is a drop in blood pressure. Breathing can stop and the body may slip into shock. If medication is not quickly administered, heart failure and death can result within minutes. Allergens in insect venom and injectable medications are more likely to cause anaphylaxis than any other allergen. Anaphylaxis is not a common reaction and can be controlled with prompt medication and the help of a physician.

The Immune System
The immune system consists of two types of white blood cells called T-cells and B-cells. These cells help the immune system defend our body by recognizing foreign and potentially harmful substances, and then releasing potent chemicals to combat the foreign invader. An allergic reaction occurs when the immune system mistakenly recognizes a harmless substance (such as pollen) and becomes sensitive to that substance. Repeated exposures to the substance, even years later, can trigger an allergic reaction.

Who gets Allergies?
The tendency to develop allergies is thought to be inherited, because they commonly develop in those who have a family history. However, it is possible for anyone to develop allergies at any age. Environmental factors can make our immune systems overly sensitive. This could then trigger allergies in people with no family history or help its onset in those that have a family history.

Primary Exposure
T-cells recognize the foreign allergen and release chemicals, which instruct B-cells to produce millions of antibodies, called IgE. (Each time a different type of allergen triggers IgE production, a new type of IgE is produced, specific to that allergen). IgE’s then attach themselves to mast cells. Mast cells with attached IgE’s can remain in the body for years, ready to react with the same allergen.

With re-exposure, allergens re-enter the body and directly contact the IgE antibodies attached to the mast cells. This stimulates the mast cells to quickly release chemicals like histamine. The release of these chemicals can cause tightening of smooth muscles in the airways; dilating small blood vessels and making them leak (resulting in warming and swelling of skin tissues); increasing mucus secretion in nasal cavity and airways; and itching.