The idea of link between hayfever and pollution is a popular one, and it owes much to research done in Japan, where public disquiet over air polution is unusually high.
Concerned about the soaring rates of allergy to Japanese cedar pollen, the predominant form of hay fever in Japan, Shigeru Takafuji of the University of Tokyo began to suspect a link with diesel-powered vehicles, which had increased from about 15,000 in 1951 to more than 5 million in 1983.
When he repeatedly injected soot particles from diesel exhaust into mice, along with an antigen, they stimulated the production of an antibody called IgE that precipitates allergic reactions. Takafuji found that the IgE was made in response to the antigen, not the soot particles, so he concluded that the diesel exhaust had merely acted as an ""adjuvant"" - something that influences the course of an immune response.
When he put the diesel particles and antigen into the noses of mice, the same thing happened: their bodies produced up to 100 times more IgE when the diesel particles were present as when they were absent. Just 1 microgram of particles given at three-weekly intervals was enough to produce this effect. (Urban commuters could inhale 500 micrograms of diesel particles every working day.)
Other Japanese researchers, looking at the distribution of hay fever, have corroborated Takafuji's laboratory studies with mice. According to their findings, allergy to Japanese cedar is commonest in those living alongside cedar-lined trunk roads with heavy traffic. More than 13% of people living on such roads suffer symptoms of hay fever in the cedar-pollen season. Among those living close to cedar forests, where the pollen in the air is equally plentiful but traffic minimal, the figure is only 5%. In farming and city areas with traffic that is lighter than on main roads, the figure is about 9%, regardless of whether pollen levels are low or high. Another Japanese study found an astonishingly high level of hay fever and other nasal allergies among children from highly polluted areas: no less than one in three showed symptoms.
The Big Sneeze, Linda Gamlin., p37-41, New Scientist 2 June 1990