In 1926, Swiss researchers surveyed the difference between city and country dwellers for hay fever occurrence. They found that people living in urban areas were ten times more likely to suffer from hay fever than were their country cousins, even though pollen densites were higher in the country. A 1985 Swiss study of 2500 people showed the country-city difference had disappeared. In 1926, the cites had polluted air, but the country air was clean. By 1985, air pollution was pervasive.
Some Japanese research seems to corroborate the Swiss view.
There more than 15 percent of the residents have hay fever symptoms. Air pollution seems to make the perfect villain, except for one glitch in the historical record. It wasn't the urban poor, forced to breathe air fouled by uncontrolled factories, who suffered the sudden surge of hay fever symptoms in the last century. It was the upper classes, who often lived under clear skies far from the smoky source of their wealth. Recent work in Britain now suggests that the aristocrats may have had problems because their upbringing, not their air, was too clean.