Allergies are an overreaction of the body’s immune system to specific substances that it misidentifies as harmful. This overreaction of the body’s immune system is known as an allergic reaction and the substances that cause it are called allergens. Potential allergens can be anything from dust mites and pollen to insect stings, fragrances, and foods such as shellfish and peanuts. Whatever the allergen, allergic reaction symptoms can be miserable, ranging from a runny nose and watery eyes to breathing problems, diarrhea, hives, and even death.

Allergens and Your Body
Your body’s immune system is a collection of cells and organs that work individually and collectively to protect your body from outside invaders such as parasites, viruses and bacteria. Your immune system is an incredibly active and efficient defense mechanism, but not a perfect one. That is why we all get colds and many people develop diseases.

Allergic reactions are caused by both an outside invader and the body making a mistake. When a generally harmless substance such as pollen enters your body, your immune system may mistakenly treat it like a harmful invader. How your body reacts next determines the symptoms you feel.
The Allergy Chain of Events

Here is what happens inside your body when an allergic reaction occurs. This is known as the allergic chain of events or the allergic cascade.

 
• The allergen enters your body where it is misidentified as a harmful and foreign substance by your specialized white blood cells that work together to identify and exterminate bacteria and viruses. These cells are known as B-cells and T-cells.  
• Your body then begins producing IgE antibodies which are proteins specifically engineered to neutralize the threat of the mis-identified allergen.  
• These IgE antibodies attach themselves to a specialized blood cell known as a mast cell (most commonly found in the body’s airways and GI tract) and lie in wait for the same substance to enter the body again.  
• When the allergy sufferer comes into contact again with the same allergen, the IgE antibodies begin breaking down the mast cells.  
• As mast cell walls are destroyed, each releases a load of chemicals, including histamine, prostaglandins, and leukotrienes, into the surrounding tissues and blood.  
• These chemicals then bind to receptors in your blood, nasal tissues and other tissues in your body, causing a host of symptoms ranging from swelling to sneezing and a runny nose to hives.  
• The release of histamine is what causes a cascade of allergy symptoms that can affect the GI tract, skin, respiratory system or cardiovascular system.

If your allergen is airborne, you will probably get an allergic reaction in your eyes, nose or lungs, causing watery eyes, a runny nose and breathing problems. If the allergen comes into contact with your skin, you may get a rash or itchy patches. If you ingest the allergen by eating a food or taking a drug by mouth, reactions can occur inside your mouth, your stomach, or your intestines.

The Genetic Factor
Allergies to specific allergens are not inherited, however, the tendency to develop an allergy is inherited. For example, if you’re allergic to cat dander there is a chance that your child will also develop an allergy, but not necessarily to cat dander. If you are allergic to a substance, chances are one in three that your child will also develop an allergy. If both parents have allergies, the child has a 65-75% chance of developing allergies. A person who is prone to allergies is described as atopic. Studies have indicated that individuals who have atopy seem to also be at greater risk for becoming asthmatic.