What is an allergy?

Many people have experienced the stuffy noses, itching eyes, and hives that may come with exposure to something as seemingly harmless as pollen or pet dander. Allergies seem to be one of the most common forms of irritation in existence. But what is the cause of an allergy? An allergy is essentially an inappropriate response by the body’s immune system to an otherwise unharmful substance. A foreign body that is misidentified as potentially dangerous can trigger a cascade of symptoms from the unpleasant to the dangerous.

Your immune system works to protect the body from potentially dangerous pathogens we may ingest, inhale or otherwise come in contact with. Its job is to recognize and deal with any foreign substances that enter the body. Common allergens (things that cause allergies, such as dust or pollen) are always dealt with by the immune system, however, in allergic individuals this process of dealing with a foreign body can spiral out of control and cause all the classic allergy symptoms.

The immune system can recognize a substance that is not native to the body and deals with it by producing antibodies, special proteins that identify and neutralize the threat. A specific type of antibody, called immunoglobin E (or IgE) is involved in allergic reactions.

IgE is an antibody that deals primarily with responding to large, extracellular threats such as, for instance, a parasitic worm. A threat like this, too large to simply be “eaten” by another cell, needs to be dealt with in a different manner. IgE attempts this by creating in the body a hostile environment for such a parasite, resulting in its death. This is achieved by causing cells in the body to release certain chemicals, most importantly a chemical called histamine, which creates symptoms such as inflammation and heat. Mucous production and coughing or sneezing are employed to remove foreign bodies from the lungs and sinuses.

Sometimes this IgE reaction can be caused by an otherwise harmless allergen instead of a real threat, and an allergic reaction is the result. Scientists are not yet sure exactly why this occurs, but this initial mistaken identity can lead to an eventual sensitization to the allergen in question. Through subsequent exposure, the body produces more antibodies specific to this allergen and the reactions tend to become more severe, creating an allergy.

The severity of this runaway immune response to an allergen will vary between individuals. Often it is as minor as itchy eyes and congestion but can become as serious as an anaphylactic shock, a potentially fatal condition. It is thought that allergies have both a genetic and environmental component involved in their formation. Some evidence suggests that exposure to allergens as a young child can increase one’s risk of developing allergies, while other research holds the exact opposite to be true. The topic remains a very active area of study.