Characterized by sneezing; rhinorrhea; obstruction of the nasal passages; conjunctival, nasal, and pharyngeal itching; and lacrimation, all occurring in a temporal relationship to allergen exposure. Prevalence in North America is 10–20% with a peak prevalence >30% occurring in the fifth decade. Commonly seasonal due to triggering by airborne pollens; can be perennial in response to allergens present throughout the year such as house dust mites and animal danders.