What is allergic rhinitis (hay fever)?

Allergic rhinitis is an allergic reaction of the upper respiratory system to a substance called an allergen, which is anything that causes an allergy. These reactions will occur either seasonally (during certain seasons of the year) or perennially (throughout the year).

Seasonal rhinitis comes and goes with the reproductive cycles of plants and fungi (mold). At certain times of the year (depending on their species and where they are located), plants release pollen into the air, and fungi release spores. People who are allergic to one or more kinds of these allergens will develop allergic rhinitis.

Tree pollen tends to be the cause of symptoms in the spring, grass pollen in the summer, and ragweed and other weeds in the fall. Fungi are suspect over a much longer period because they release their spores from late March until November.

Weather influences how severe allergy symptoms will be because it affects the daily pollen count. Pollen counts tend to be at their highest on warm, dry, and breezy mornings, and at their lowest on rainy, cool days. Generally, your allergic reaction will be severe or mild, depending on the rise and fall of the pollen count.

As the name suggests, perennial rhinitis occurs all year round. It is caused by allergens whose production is not tied to any seasonal cycle. Common examples are dust mites, animal dander, and molds. Dust mite allergens can be found in pillows, down-filled clothing and bedding, draperies, upholstery, and thick carpeting. Symptoms will be steady if you come into contact with the allergen every day, but they can come and go if you only have occasional contact. It also is possible that if you have a constant reaction to a perennial allergen that you may actually have a seasonal allergy.

How common is allergic rhinitis (hay fever)?

This condition affects approximately 10% of the U.S. population (roughly 30 million people) and is the most common allergic disorder in the country. No one knows why some people suffer from allergies and others do not. Some evidence suggests that allergies could be a hereditary (inherited) trait. Other evidence links allergic rhinitis to asthma and eczema. People who suffer from these diseases are more likely to develop allergic rhinitis, too.

What causes the symptoms of allergic rhinitis (hay fever)?

The symptoms of allergic rhinitis are caused by your immune system protecting itself from what it identifies as an invading substance. Most evidence suggests that genetics (heredity) determine whether your body will mount this kind of defense.

This allergic response begins with the production of allergic (IgE) antibodies (special type of proteins produced by the body). The job of these antibodies is to find molecules of the offending substance in the bloodstream and tissues and to escort them to the body's mast cells (a type of allergy cell) for destruction. As the mast cells destroy the allergens, a chemical called histamine is released into the bloodstream and certain mucous membranes (specifically, the lining of the nose or eyes).

Histamine makes the sinuses and eyelids red and swollen. It also triggers the sneezing reflex. The swelling is designed to block more of the allergens from entering the body, and sneezing is a method of getting rid of them. Histamine also causes itching and allows fluids to enter the nasal tissue, which results in congestion (stuffiness) and a runny nose.