Allergic rhinitis is a common health problem for which many patients do not seek appropriate medical care. Although not a life-threatening condition in most cases, it has a substantial impact on public health and the economy.
According to findings in a recent study, the total estimated cost of allergic rhinitis in 1994 was between 1.2 and 1.5 billion dollars.  The illness resulted in more than 6 million missed work days, 2 million missed school days, and 28 million reduced-activity days. These figures are certainly higher today because of the higher cost of new medications and the increasing prevalence of the condition.
Because the nose is the most common port of entry for allergens, in patients with allergies, signs and symptoms of allergic rhinitis, not surprisingly, are the most common complaints.
Four types of hypersensitivity responses exist, as initially classified by Gell and Coombs and later modified by Shearer and Huston. Individuals with allergic rhinitis are thought to have type I reactions.
After initial exposure to an antigen, antigen-processing cells (macrophages) present the processed peptides to T helper cells. Upon subsequent exposure to the same antigen, these cells are stimulated to differentiate into either more T helper cells or B cells. The B cells may further differentiate into plasma cells and produce immunoglobulin E (IgE) specific to that antigen. Allergen-specific IgE molecules then bind to the surface of mast cells, sensitizing them.
Further exposures result in the bridging of 2 adjacent IgE molecules, leading to the release of preformed mediators from mast cell granules. These mediators (ie, histamine, leukotrienes, kinins) cause early-phase symptoms such as sneezing, rhinorrhea, and congestion. Late-phase reactions begin 2-4 hours later and are caused by newly arrived inflammatory cells. Mediators released by these cells prolong the earlier reactions and lead to chronic inflammation.
Approximately 39 million Americans are reported to have allergic rhinitis. From various studies, 17-25% of the population in the United States are estimated to have the condition.
Allergic rhinitis can significantly decrease the quality of life and impair social and work functions, either directly or indirectly, because of the adverse effects of medications taken to relieve the symptoms.
Males and females tend to be affected by allergic rhinitis in fairly equal proportions. A study by Cazzoletti et al found gender-associated age-based differences in the prevalence of self-reported allergic and nonallergic rhinitis, with allergic rhinitis showing an age-based decrease in prevalence that was comparable in males and females (from 26.6% in persons aged 20-44 years to 15.6% in persons aged 65-84 years), and nonallergic rhinitis showing an age-based decrease in prevalence among females (from 12.0% in females aged 20-44 years to 7.5% in females aged 65-84 years) and roughly the same prevalence in younger and older males (10.2% in males aged 20-44 years and 11.1% in males aged 65-84 years). 
Allergic rhinitis appears mainly to affect individuals younger than 45 years.
The condition may begin to appear in patients as young as 2 years and usually reaches a peak in those aged 21-30 years.
It then tends to remain stable or slowly decrease until patients are aged 60 years, when again the prevalence may increase slightly.
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