ABSTRACT
In the mid-1800s when Charles Blackley began to investigate hay fever, there were many theories regarding its causation. The theories at the time included that it was caused by inhalation of benzoic acid or the odor of hay (or other odors); that it was due to the action of ozone, the effects of dust, or the influence of light and heat; and finally that it was caused by inhaling pollen. By experimenting on himself, Blackley was able to exclude all causative mechanisms other than pollen and dust. During his investigations, which included various challenges, not only did he provoke symptoms of allergic rhinitis, but on many occasions he also provoked an attack of asthma. His observations of those who suffered from the disease suggested that it was most predominant in well-educated people. He observed a lack of symptoms among farming classes, which he attributed to poor education and the possibility that they had developed immunity because of their great exposure to pollen. Even at that time he was concerned that hay fever was increasing, which he attributed to increased education and a change in the proportion of people involved in farming activities (1).
