Dust, spores and animal dander are believed to be the allergens that cause hay fever. In the past, people associated the harvesting of fields of hay along with sneezing and chronic fever with the therm "hay fever".

Today, however, the belief that 'hay fever' comes from harvesting of fields of hay is believed to be a misnomer. The experts say that contact with a field of hay should not be associated with fevers.

The more common term for hay fever, today, is allergic rhinitis. The term has been introduced because it is a more appropriate term medically. 'Rhinitis' refers to the irritation of the nasal passages that is connected to sneezing, nasal congestion, itchy eyes and nose, runny nose and excess tears. Sometimes, when put together, these symptoms can bring on an unusually high temperature.

When the body's immune system is attached by these allergens, that's when hay fever occurs. Within the body's immune system, there is a productive substance called the 'immunoglobuline E' or IgE. Allergic rhinitis begins when the antibodies (allergens) begin to hurt mast cells. The group of cells are sometimes unprotected by IgE because they are so many that the IgE supply can't cover them all up against all of the antibodies.

When mast cells are infected, they secrete allergic substances toward tissues and other body cells. One of these substances is histamine. Histamine is a very strong and irritating substance that cause itching and swelling to tissues and leaking of fluid from cells.

In the long run, these substances, like histamine, could trigger a lot more mechanisms to cause more serious disorders like tightening of the throat, loss of voice, and more seriously, asthma. Sometimes, sufferers of hay fever experience muscle spasms and lung contraction.

Allergic rhinitis is also proven to be specifically caused by proteins. Individuals who always come in close contact with plants might be infected with proteins called pollens, the known male sex cells in weeds, trees, and grasses. Pollen is usually invisible since it is only about 4 microns in diameter.

Even though pollen is so small, and practically invisible, it is considered a very potent source of allergies. These pollens will rest on nasal passages and affect the entire respiratory tract. This, in turn, causes severe allergic reactions.