Allergic rhinitis is the most common of the allergic disorders, affecting at least 10% and perhaps more than 20% of the United States population. 27,65 It can affect individuals of all ages, beginning even in infancy. Although immunoglobulin E (IgE) production tends to decrease in older persons, allergic rhinitis does affect this age group also, and very occasionally may begin in elderly individuals. Allergic rhinitis is most prevalent in children and adolescents, however, and onset occurs before the age of 30 years in most patients. 72 Allergic rhinitis is the most common chronic illness in persons 30 years of age and younger and is the fifth most common chronic illness in the overall population. 74 Allergic rhinitis manifests as a perennial, seasonal, or episodic disorder, often with significant variation of symptoms and severity from day to day. Seasonally increased difficulties may overlap chronic perennial symptoms. The symptoms may vary in severity from trivial to disabling. Although nasal symptoms may predominate, other non-nasal and systemic symptoms may contribute to substantial dysfunction, resulting in lost school and work days, 65,92 interference with normal day-to-day functioning, loss of intellectual 8,90 and physical productivity, and general diminution of quality of life. 4 Allergic rhinitis is not life-threatening, but it does threaten the quality of life. Recently appreciated, also, is its association and possibly pathogenic relationship with chronic sinusitis, otitis media with effusion, and bronchial asthma. 4,93,95 The costs for allergic rhinitis are high. The total cost of allergic rhinitis was estimated to be $1.8 billion in 1990 61 and $2.4 billion in 1995. 82 These figures do not include the costs of associated disorders. Approximately 50% of persons with symptoms do not go to a physician for treatment, however. (One important reason seems to be concern about the side effects of prescribed agents.) 49 Tolerance for symptoms varies considerably among patients, with many patients choosing simply to endure the symptoms despite suboptimal functioning. Thus, true costs for all patients with allergic rhinitis are probably far in excess of the estimates given. Allergic rhinitis is associated with several other conditions, some of which are probably caused by the mechanical obstruction associated with nasal tissue inflammation (e.g., otitis media with effusion caused by eustachian tube dysfunction, and chronic sinusitis). 4 In children, facial bone abnormalities can develop as a result of chronic mouth breathing from allergic rhinitis with nasal obstruction. Nocturnal nasal obstruction can cause snoring, obstructive sleep apnea, poor sleep patterns, and daytime somnolence. 21,84 Nasal polyps may develop, especially in adults, although polyps are equally likely to occur in patients without an allergic basis for their rhinitis. Hyposmia or anosmia with associated diminished sense of taste may occur with allergic rhinitis and can be associated with a decreased appetite. There may be complaints of abdominal discomfort, especially if postnasal drainage is a significant symptom, and especially in children. Patients with allergic rhinitis may be more susceptible to viral upper respiratory tract infections. 4,6 Allergic conjunctivitis frequently occurs in patients with nasal allergies, and asthma is a common comorbid condition with allergic rhinitis. Asthma may be found in up to 15% of persons with allergic rhinitis, 91 and most patients with asthma have allergic rhinitis. 4,88,95 A substantial number of patients with allergic rhinitis have exercise-induced bronchospasm. 93 Further, as a group, patients with allergic rhinitis without asthma symptoms tend to have increased bronchial responsiveness, 93 to exhibit an increase in diurnal variation of peak flows, 78 and appear to have an increased risk of developing asthma. 88 Thus, allergic rhinitis further contributes to increased morbidity and to the costs associated with various other disorders. Symptoms of allergic rhinitis, including nasal congestion, sneezing, rhinorrhea, and nasal itching can occur singly or in various combinations; associated symptoms may include postnasal drainage and itching of the eyes and of other non-nasal areas such as the palate, throat, face, neck, scalp, and external auditory canals. Systemic symptoms can include headache, torpor, malaise, somnolence, fatigue, decreased energy, inability to concentrate, and irritability. Feelings of embarrassment and frustration over symptoms may occur. 4,8 Emotional and learning problems in children have been noted. 8,90 Central nervous system effects may be subtle but still interfere with intellectual functioning at school or work. These CNS effects can be ameliorated or eliminated with the use of appropriate therapy, 103,104 but some types of treatment, such as first-generation antihistamines with their frequent attendant sedative effects, may intensify these problems. 82