Traditionally, people allergic to grass pollen have been advised to watch for high pollen concentrations during the day, and to reduce their outdoor activities during daylight, but new research from Universities across Europe shows the situation might be more complex and avoiding pollen more difficult.  

A new study led by researchers from Aarhus University, Denmark, which featured contributions from the Universities of Worcester, Vienna and Roskilde shows the difficulty of avoiding grass pollen.

The researchers conducted intensive measurements over three years and identified 'peak times' for pollen. These times are complicated and vary widely over the course of the season; plotted on a graph, pollen releases appear to be lumped together in one four hour 'peak period' during mid-season, but in early and late season have two separate periods where concentrations are higher (8-10am and again between 4-6pm in early summer, then 8am-2pm and 4-6pm later in the season).

So, how should people react to these complicated patterns? Dr. Robert Peel, Aarhus University, explained, "People should avoid being outdoors during the peak hours in periods one and two, especially between 4pm and 8pm. Later in the summer, allergy sufferers should avoid being outdoors in the middle of the day."

Different species have different patterns

Concentrations of grass pollen are influenced by many factors, the most important being the weather, though this affects different grass species in different ways. Denmark alone is home to 230 species of grass; the UK has around 160 species.  

Changes to the environment affect the release of pollen, though variables include temperature changes either the day before or on the day of release and rainfall affects different grasses differently; some plants stop releasing pollen when it rains whereas others release their pollen in response to rain. Each grass species flowers intensively for approximately one-two weeks, and the total season is around two months, which is why pollen levels are so complicated to predict, but in general, people react more or less in the same manner to the pollen of all grasses, the researchers said.