section_path: Epidemiology
section_name: Epidemiology
paragraph_text: Epidemiology
  
  The allergic diseases—hay fever and asthma—have increased in the Western world over the past 2–3 decades. Increases in allergic asthma and other atopic disorders in industrialized nations, it is estimated, began in the 1960s and 1970s, with further increases occurring during the 1980s and 1990s, although some suggest that a steady rise in sensitization has been occurring since the 1920s. The number of new cases per year of atopy in developing countries has, in general, remained much lower.