When John Bostock first described hay fever in 1819 the condition was rare, but allergy has now reached epidemic proportions, with almost one in two people in the developed world exhibiting an allergic response to some common environmental factor. Most allergic diseases are linked to atopy, the predisposition to generate the allergic antibody IgE to common environmental agents. Because IgE is able to sensitise mast cells anywhere in the body, atopic individuals often express disease in more than one organ. Although current treatments are able to control symptoms, allergy still causes appreciable misery. There is an urgent need for new approaches to more effectively treat allergic responses and prevent their occurrence. This review focuses on some exciting new developments based on a clearer understanding of the underlying cellular and mediator mechanisms and how the human body interacts with the changing environment.