What are allergies?
An allergic reaction is a specific immunological reaction to a normally harmless substance, one that does not bother most people. People who have allergies often are sensitive to more than one substance. Types of allergens that cause allergic reactions include pollens, dust particles, mold spores, food, latex rubber, insect venom, or medicines.

Pollen
Each spring, summer, and fall, tiny particles are released from trees, weeds, and grasses. These particles, known as pollen, hitch rides on currents of air. Although their mission is to fertilize parts of other plants, many never reach their targets. Instead, they enter human noses and throats, triggering a type of seasonal allergic rhinitis called pollen allergy, which many people know as hay fever or rose fever (depending on the season in which the symptoms occur). Of all the things that can cause an allergy, pollen is one of the most widespread. Many of the foods, drugs, or animals that cause allergies can be avoided to a great extent; even insects and household dust are escapable. Short of staying indoors when the pollen count is high -- and even that may not help -- there is no easy way to evade wind born pollen.

Mold
Along with pollens from trees, grasses, and weeds, molds are an important cause of seasonal allergic rhinitis. People allergic to molds may have symptoms from spring to late fall. The mold season often peaks from July to late summer. Unlike pollens, molds may persist after the first killing frost. Some can grow at sub-freezing temperatures, but most become dormant. Snow cover lowers the outdoor mold count dramatically but does not kill molds. After the spring thaw, molds thrive on the vegetation that has been killed by the winter cold.

In the warmest areas of the United States, however, molds thrive all year and can cause year-round (perennial) allergic problems. In addition, molds growing indoors can cause perennial allergic rhinitis even in the coldest climates.

Dust Mite
Dust mite allergy is an allergy to a microscopic organism that lives in the dust that is found in all dwellings and work places. Dust mites are perhaps the most common cause of perennial allergic rhinitis. Dust mite allergy usually produces symptoms similar to pollen allergy and also can produce symptoms of asthma.

What is house dust?
Rather than a single substance, so-called house dust is a varied mixture of potentially allergenic materials. It may contain fibers from different types of fabrics; cotton lint, feathers, and other stuffing materials; dander from cats, dogs, and other animals; bacteria; mold and fungus spores (especially in damp areas); food particles; bits of plants and insects; and other allergens peculiar to an individual home.

Chemical Sensitivity
Some people report that they react to chemicals in their environment and that these allergy-like reactions appear to result from exposure to a wide variety of synthetic and natural substances, such as those found in paints, carpeting, plastics, perfumes, cigarette smoke, and plants. Although the symptoms may resemble some of the manifestations of allergies, sensitivity to chemicals does not represent a true allergic reaction involving IgE and the release of histamine or other chemicals.

Air Conditioners and Filters
When possible, an allergic person should use air conditioners inside the home or in a car to help avoid pollen and mold allergens from entering. Various types of air-filtering devices made with fiber glass or electrically charged plates may help reduce allergens produced in the home. These can be added to the heating and cooling systems. In addition, portable devices that can be used in individual rooms are especially helpful in reducing animal allergens.