Biologic Mechanisms Leading to Allergic Rhinitis.

The body's immune system is designed to produce various factors to fight foreign substances, including bacteria, viruses, and other proteins that the immune system perceives as threatening. An allergic response occurs when the body's immune system over-responds, or is hypersensitive, to specific non-infectious particles. Some experts believe that this hypersensitivity response originally developed in humans as a way of fighting parasites and worms. Common allergens include plant pollens, molds, dust mites, animal dander, industrial chemicals, foods, medicines, and insect venom. Among the important components of the immune system are the antibodies, also known as immunoglobulins, which are produced by lymph tissue. A key player in the allergic response is the antibody known as immunoglobulin E (IgE), which is overproduced in certain people, usually those with an inherited susceptibility. During an allergic attack, these antibodies attach to cells known as mast cells, which are generally concentrated in the lungs, skin, and mucous membranes. Once IgE binds to mast cells, these cells are programmed to release a number of chemicals. One of these chemicals, histamine, causes dilation of blood vessels, skin redness, and swollen membranes; when these effects occur in the nose, they can cause the symptoms of allergic rhinitis.

Triggers of Seasonal Allergic Rhinitis (Hay Fever or Rose Fever).

Seasonal allergic rhinitis is commonly, although incorrectly, called hay fever or rose fever, depending on whether it occurs in the late summer or spring. No fever accompanies this condition, and the allergic response is not dependent on either hay or roses. Ragweed is the most important cause of allergic rhinitis, affecting about 75% of allergy sufferers. One plant can release one million pollen grains a day. Ragweed is everywhere in the U.S., although it is less prevalent along the West Coast, southern Florida, northern Maine, Alaska, and Hawaii. The effects of ragweed in the northern states are first felt in late August until the first frost. Other grasses and trees that release very small pollen grains are also culprits. People who are sensitive to tree pollen usually have symptoms in late March and early April. Grasses affect people in mid-May to late June. Mold spores that grow on dead leaves and release spores into the air are also common allergens. Depending on the allergen, the risk for an allergy attack is highest at different times of the day. Ragweed allergies tend to strike before midday; grass allergies are experienced more in the late afternoon; and mold spores may peak on dry windy afternoons or on damp or rainy days in the early morning.

Triggers of Perennial (Year-Round) Allergic Rhinitis.

Allergens in the house, such as house dust mites and pet dander, can cause year-long allergic rhinitis, called perennial rhinitis. Molds growing on wallpaper, house plants, carpeting, and upholstery are also perennial allergens