The immediate cause of hay fever is a reaction to pollen (the powder carried from flower to flower by bees that makes plants fertile). If your body has an allergy to pollen, then in the spring and early summer when there is the most pollen in the air, your body will see it as a possible threat and try to expel it. The sneezing and runny nose that go with hay fever are ways your body uses to get rid of the pollen.

It's very common to have some reaction to a high pollen count - many of us sneeze more in the spring - but severe hay fever is often linked to other conditions. You are more likely to have hay fever if you suffer from asthma or if it is in your family, or have a skin complaint such as eczema. There is also some evidence that lifestyle factors, such as being around tobacco smoke - especially in childhood - can play a part.