Hay Fever Causes

Rhinitis is inflammation of the mucous membranes in the nose. It’s often caused by common colds and other viral infections. Allergic rhinitis, also known as hay fever, is the most common form of rhinitis. It causes irritation of the nasal membranes due to different airborne allergens.

An allergy is an immune system response. Your immune system’s job is to protect you from outside invaders such as viruses, bacteria, and parasites. Sometimes your immune system mistakes something harmless for an invader. When this happens, you develop antibodies to fight the harmless substance.

The antibodies involved in hay fever are immunoglobulin E (IgE) antibodies, which are the normal antibodies the body makes to fight parasitic infections. The first time you are exposed to an allergen like pollen or dust mites, your body makes IgE antibodies to "defend" against it. This is called sensitization. The next time you are exposed, those IgE antibodies go to work to destroy the allergen. They do this by inducing the release of histamines and other chemicals that cause the inflammation and other symptoms of allergy.

Seasonal hay fever is usually caused by outdoor allergens. It commonly affects people from spring through fall, depending on when certain plants and trees release pollen into the air. Allergens that frequently cause seasonal hay fever include:

• tree pollen (in the spring)
• grass pollen (in the late spring and summer)
• weed pollen (in the fall)
• fungi and mold spores (in the warmer parts of the year)

Year-round (perennial) hay fever is usually caused by allergens other than pollen, most often those found in the home. These include the following:

• animal dander: Cats in particular are the cause of allergy symptoms for many people because they frequently lick their coats. This releases dander and inflammatory proteins from their saliva into the air. Unlike dogs, cats tend to closely share living spaces with their owners and houseguests.
• indoor mold: Mold grows in damp, dark areas of a home. A kitchen can be especially problematic for perennial rhinitis sufferers, who are more likely to have both outdoor and indoor allergens affect them.
• dust mites. These are microscopic bugs that live in house dust. They may be found in bedding, upholstery, and carpets.
• cockroaches. These usually live in moist, warm hiding areas, such as near standing water or sweating pipes, under the sink, and wall or floor cracks. Cockroaches tend to live near food supplies. They also eat newspapers, book binding, and wallpaper paste.

Perennial hay fever may also be caused by extreme sensitivity to plant pollens throughout the seasons.

Once triggered by any of these allergens, the allergic reaction is caused by the release of histamine and other chemicals. These cause the swelling of nasal and eye tissues, the secretion of mucus, and, possibly, the constriction of airways.

Some factors that may increase your risk of developing hay fever are described below.

High IgE Levels

Hay fever usually begins at an early age. Children under 6 years old who are tested for immunoglobulin E (IgE) levels will be at risk for hay fever if serum IgE is greater than 100 international units (IU) per milliliter (mL). 

Family History

A family history of hay fever or asthma increases your risk for developing allergies.

Environmental Exposure

Living or working in an environment that consistently exposes you to allergens, such as dust mites and pollen, can greatly increase your risk of developing hay fever.