Researchers at Northumbria University have found that one in three runners in next month's London Marathon will suffer from allergic reactions (for example from tree pollen) after the event.
Post-marathon sniffles are a common complaint among runners, but they are often put down to infections taking advantage of a depleted immune system caused by the effort involved.
Now, however, the Northumbria University team led by Dr Paula Robson-Ansley has shown how far symptoms such as itchy eyes, a runny nose and congestion can be attributed to allergic reactions.
150 runners in last year's London Marathon completed a health questionnaire, gave a blood test, and reported on the symptoms they experienced up to three days after the event.
Eye and nose problems were reported by 61% of the runners sampled and subsequent blood tests to determine whether immunoglobulin E antibodies were present - the telltale sign of an allergic reaction - revealed that 35% of the runners were experiencing an allergy.
The study also found that 14% were specifically allergic to tree pollen. Tree pollen is particularly high in London in April as this is when pollen from High Birch and London Plane trees is released and tree-pollen counts had been high on the day of the 2010 marathon itself.
In a further result that has implications for next year's Olympic Games, Dr Robson-Ansley found that 29% of the runners were showing an immunoglobulin E reaction to grass pollen.
"The Olympics are taking place during the peak grass-pollen period," she says, "so, if almost three out of ten people are potentially allergic to this common aeroallergen, it is a priority to have Olympic athletes tested before the Games so an appropriate treatment regime can be put in place."