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Pollen levels, often referred to as the pollen count, vary with the time of year and weather. In general:
Types of pollen
Tree pollen (e.g. birch) is released during spring. However, trees such as hazel and yew may cause symptoms as early as February, while oak pollen may persist into June.
Grass pollen is released at 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.