It’s estimated that almost 30 percent of people in industrialized countries are allergic to pollen, with urban areas hit the hardest despite their lack of vegetation.

From the early 1970s to the present day there has been a sharp increase in the number of people suffering from allergy attacks. Åslög Dahl, a researcher in the University of Gothenburg’s Department of Biology and Environmental Science, explains why.

“The hypothesis is based on our decreasing tolerance to pollen,” says Dahl. “Children develop their immune system in symbiosis with bacteria in the digestive tract during their first four years of life. To become resistant, bacteria must be able to thrive and form a good chemical environment within the gut. This is more difficult for children who grow up in very clean environments.”

Air pollution also affects the tendency to be allergic to pollen. A study conducted in 2010 revealed that the demand for antihistamines (medicine for allergies) ­escalated when allergenic pollen existed in connection with unclean air.

“Ground-level ozone, nitrogen dioxide and particles can cause inflammation of the bronchi, increasing sensitivity to external influences,” explains Dahl. “We have seen that diesel particles damage the walls of the lungs, allowing allergens to get in.”

How will pollen allergies develop in the future?

“I imagine that this development will soon reach a ceiling, or that perhaps it already has. I also believe that the situation will soon look very different. Climate change will lead to new types of vegetation and pollen – and no one can say how this will affect allergies.”