What is hay fever and why is it so called?

Hay fever is a form of allergy belonging to a group of maladies including hives, asthma and skin problems caused by protein sensitization. During certain seasons, many plants, grasses release their pollens into the air in large quantities. A person is said to have hay fever when he / she is sensitive to these pollens and other substances present in the air. It is called hay fever because the symptoms of the disease appear during spring and fall in England.