Being aware of the pollen count, and therefore the pollen risk, can help hay fever sufferers prepare. The pollen count is based on readings from pollen monitoring stations run by the Met Office. Special equipment blows air at a specified rate onto an adhesive strip on a rotating drum. Pollen forecast levels are based on the number of pollen grains seen on the strip when analysed under a microscope.

Airborne pollen levels tend to be highest in the morning as they rise in the warming air, and again at the end of the day, sinking in the cooling air. Drier and/or windy conditions will also increase symptom risk.

Allergy UK warns of the misconception that thunderstorms and heavy rain will clear the air of pollen and particles. €On the contrary, such conditions often have the opposite effect €“ a medical phenomenon called thunderstorm asthma,€ it says. €The phenomenon is still not fully understood by scientists but is known to increase A&E visits and ambulance calls.€

It is possible that the weather conditions break up pollen aggregates, making them lighter and more likely to be airborne and capable of being inhaled.