Allergies In Depth: Why Does the Body Respond This Way?

Many people are affected by seasonal allergic rhinitis (SAR). Ten to twenty five percent of the U.S. population experience nasal congestion, runny nose, sneezing, itchy watery eyes and scratchy throat that characterize allergic rhinitis. Males and females are equally affected. Personal and family history of asthma and atopic dermatitis are risk factors for this condition. The symptoms of allergic rhinitis are provoked by allergens in the environment. When people have allergic rhinitis during particular seasons, such as the spring and fall, it is called seasonal allergic rhinitis. The typical allergens involved in SAR are pollens: trees in the spring, grass in the summer and weeds in the fall.

Before the body becomes "allergic" to something, it usually needs to be exposed or sensitized to a foreign particle to realize it is foreign. The sensitization process begins with the first exposure to an allergen. This begins the synthesis and release of antibodies (specifically IgE) which attach to specialized immune cells called basophils. Once this connection is made between IgE and the basophils, they are "sensitized" to a particular allergen. When the body is re-exposed to an allergen, the allergen travels to basophils and binds to the IgE antibody. This produces an allergic or hypersensitivity reaction which involves the release of many immune chemicals. These are histamine, serotonin, bradykinin, leukotrienes, platelet activating factors, eosinophil chemotactic factor of anaphylaxis, neutrophil chemotactic factor of anaphylaxis, prostaglandins and thromboxanes. Thus, when the body is exposed to foreign particles, the immune system mounts an attack of the "invaders" by releasing an "army" of immune cells and chemicals into the bloodstream.

The immune chemicals are responsible for the uncomfortable symptoms of allergic rhinitis. Histamine causes smooth muscle contraction, mucous secretion and the dilation and leakage of blood vessels. This causes narrowing and congestion of the nasal passages, trachea and bronchi as well as swelling of the skin. Serotonin increases smooth muscle contraction, breathing rate and the body's response to histamine. Bradykinin acts like histamine, but to a much smaller degree. Leukotrienes also cause the same symptoms as histamine but the effects are slower and longer lasting. The platelet activating factors (PAFs) induce the breakdown of platelets. Platelets are needed for blood clot formation and when they are destroyed by PAFs, blood becomes thinner and flows more easily, thus causing congestion and easier transport of immune cells and chemicals to the site of attack. The chemotactic factors of anaphylaxis help attract eosinophils and neutrophils to the site of attack to help fight the allergen. Eosinophils release antihistamine substances and neutrophils eat damaged cells. Lastly, prostaglandins and thromboxanes dilate blood vessels and constrict airways as well.

Understanding the pathophysiology of SAR has led to the development of many treatments for "allergies." Antihistamines (Benadryl, Claritin, and Allegra) fight the histamine response and are medications used to prevent and treat allergy symptoms. Inhaled antihistamines (Astelin) and steroids (Flonase, Nasarel, Nasonex and Rhinocort) specifically help alleviate nasal stuffiness and drainage. People may also find the leukotriene "blockers," cromolyn and Nasalcrom, helpful.

Because SAR can be quite debilitating and the allergens are often hard to control, prevention is key. Avoiding the allergens that cause the symptoms is the first step towards prevention. If it is difficult to determine the specific allergen through observation (realizing that one gets a stuffy nose each time he/she is exposed to cats), it is helpful to undergo skin allergen testing to determine the exact allergen. It is much easier to avoid the problematic allergen, when the actual allergen is known. If the allergen cannot be avoided, the next step is to prevent the immune system from reacting to the "invader." This may be accomplished by taking nutritional supplements or medications. The medications previously mentioned may be taken preventively to avoid rhinitis or therapeutically to treat the symptoms once they have started.