Hay fever, otherwise known as seasonal allergic rhinitis, is an allergic reaction to airborne substances such as pollen that get into the upper respiratory passages - the nose, sinus, throat - and also the eyes.

Hay fever is the most common of all the allergic diseases - about 15 per cent of the population in industrialised countries suffer from this condition. Symptoms usually appear in childhood first and then lessen by the age of 30 or 40.

Perennial allergic rhinitis is a similar allergy that occurs all year round and is caused by things such as house dust, mites and pets. However the predominant allergen changes from time to time.

• Itchy and watery eyes
• Frequent sneezing, a bunged up or runny nose
• Itching on the roof of the mouth
• Coughing
• Wheezing or a burning sensation in the throat.