If you have hay fever, you may be allergic to pollen from grasses, weeds or trees, and also possibly to moulds that are carried in the air, usually during the spring and summer months. Allergens produced by these plants and moulds, for example pollen, can cause an allergic reaction in susceptible people whose immune system mistakes the allergens for harmful invaders such as viruses.

Hay fever, asthma, food allergy and eczema are related allergic conditions and the tendency to develop them seems to run in families. This inherited predisposition is called atopy and it means your body produces a certain type of antibody in response to allergens which isn't produced in non-allergic people. You may have one or more of these symptoms as follows:

-- sneezing
-- a blocked or runny nose (rhinitis)
-- itchy eyes, nose and throat
-- headaches.

As a result of these symptoms, you may find it difficult to concentrate or sleep properly. In some people, hay fever allergens may also trigger asthma. If you have hay fever-type symptoms all year round, you may also be allergic to house dust mites, pet hair and moulds. This is called perennial allergic rhinitis.