Pollen is released by certain plants €“ particularly trees and grasses €“ as a way of reproducing. Pollen levels (known as the pollen count) vary according to the time of year and the weather. There are about 30 types of pollen that may trigger hayfever symptoms in susceptible individuals, and each type has its own unique size and structure.

Someone may find they are allergic to grass pollen but not tree pollen, for example, and this will determine when they experience symptoms. Generally speaking, tree pollen is released during spring €“ birch is a common culprit at this time of year. However, trees such as hazel and yew, for example, may cause symptoms as early as February, while oak pollen may persist into June.

Grass pollen is released during the end of spring and the beginning of summer and affects around 90 per cent of hayfever sufferers. Weed pollen, such as nettle, is released from early spring through to late autumn. Symptoms during the damp, cooler days of autumn may be triggered by mould and fungal spores rather than pollen. In general, the higher the pollen count, the more troublesome hayfever symptoms will be. During the pollen season, plants release pollen early in the morning.

However, on sunny days, the pollen count peaks in the early evening. The pollen count tends to be higher on humid days with a gentle breeze as this helps pollen to spread, while rain can wash pollen out of the air, bringing relief to sufferers. Many newspapers, weather forecasts and websites offer daily pollen counts during the main hayfever season. Keeping track of these figures may help sufferers plan appropriate treatment.