Hayfever sufferers are much more likely to have a car crash.
Scientists have discovered that when pollen levels are increasing, there is a six per cent increase in fatal road incidents.
With every one per cent of airborne allergens circulating, the amount of car crashes went up by two per cent.
Researchers from Wayne State University, in Detroit, Michigan, said: "This is the first study [on] the extent to which allergies due to seasonal pollen affect traffic fatalities.
"We find novel evidence that traffic fatalities increase on days in which the local pollen count is particularly high.
"These effects are driven by cognitive impairments that arise as a result of seasonal allergies.
"We hypothesise that exposure to pollen impairs cognitive ability and reaction time."