Allergies are triggered by substances called allergens. Each year, millions of people suffer from seasonal allergy symptoms such as nose and sinus congestion, itchy, runny nose and itchy, watery eyes. However, many also suffer from perennial allergies, which result in symptoms throughout the year. Perennial allergies are triggered by indoor allergens, including house dust mite droppings, animal dander, cockroach droppings and indoor molds.

House dust mites
House dust is composed of small particles of plant and animal material in the home. While this mix is not appealing to us, microscopic creatures called house dust mites thrive in it. The droppings of these mites are the most common trigger of perennial allergy and asthma symptoms.

Dust mites are found throughout the house, but they especially thrive in high humidity and in areas where human dander (dead skin flakes) is located.

To reduce dust mites, it is important to keep humidity below 50% throughout the home by using a dehumidifier or central or window air conditioning. Wall-to-wall carpeting should be removed as much as possible, especially if it is laid over concrete floors. Hardwood, tile or linoleum is better for people with allergies. Washable throw rugs may also be used if they are regularly washed in hot water or dry cleaned.

Because people spend more time in the bedroom than in any other room, it is essential to reduce mite levels there. Encase mattresses, box springs and pillows in airtight, zippered plastic or special allergen-proof fabric covers - all are available in many national stores. Bedding should also be washed weekly in hot water (55¡ÆC) and dried in a hot drier. For waterbeds, regularly wash the mattress pad on top of the bed. Comforters and pillows made of natural materials such as down feathers or cotton should be covered with allergy-proof encasings.

Weekly vacuuming can help to further remove dust mites. People with allergies should use a vacuum with a HEPA (high-efficiency particulate) filter or a double bag, since using a standard or water-filtered vacuum cleaner stirs dust up into the air. Allergic individuals should also wear dust masks.

Animal dander
Contrary to popular belief, people are not allergic to an animal's hair, but rather, to a protein found in the saliva, dander (dead skin flakes) or urine of an animal with fur. These proteins are carried in the air on very small, invisible particles, which can land on the lining of the eyes or nose, or be inhaled directly into the lungs. Usually, symptoms will occur quickly, sometimes within minutes after exposure to the animal. For some people, symptoms may build and become most severe eight to 12 hours after they have had contact with the animal.

A cat or dog produces a certain amount of allergen per week, and this amount can vary from animal to animal. All breeds are capable of triggering symptoms - there are no "hypoallergenic" breeds of cats or dogs. People with severe allergies can even experience reactions in public places if dander has been transported on pet owners' clothing.

The most effective way to combat symptoms of animal allergy is to remove the pet from the home and avoid any contact. Keeping an animal outdoors is only a partial solution, since homes with pets in the yard still have higher concentrations of animal allergens. Before you get a pet, spend time with someone else's dog or cat to determine if you're allergic. If you already have an animal to which you or a family member is allergic, try to place it with a caring, non-allergic friend or relative. Although this separation can be difficult, it is best for the health of you or your allergic family member. You may also consider getting a pet such as a turtle, hermit crab, fish, snake, or other animals without fur or feathers.

If you cannot avoid exposure to the animal that causes your allergy symptoms, try to minimize contact. Most importantly, keep the pet out of the bedroom and other rooms where people with allergies spend a great deal of time. Some studies have demonstrated that bathing dogs or cats on a weekly basis may reduce the amount of allergens that are shed in the home. While dander and saliva are the source of cat and dog allergens, urine is the source of allergens from rabbits, hamsters and guinea pigs; ask a non-allergic family member to clean the animal's cage.

Vacuuming is not effective in decreasing animal allergens, because it does not clean the lower levels of the rug. In fact, it can stir up small allergen particles, which can also move right through the vacuum. Using a HEPA vacuum filter or double bags may help. As with dust mites, the best solution is to have a hardwood floor, tile or linoleum. Replace bedding and carpeting that has animal dander in it. It can take weeks or months for fabrics to come clean of allergens, and animal allergens may persist for a year or more after the animal has been removed.

Cockroaches
Cockroaches have been around for more than 300 million years. Most live in warm, tropical climates, but various species dwell in the offices and homes of humans. Cockroaches are not just an unwelcome visitor in the home - a protein in their droppings is a primary trigger of asthma symptoms, especially for children living in densely populated, urban neighborhoods. To reduce asthma symptoms, it is important to eliminate cockroaches.

Block areas where roaches could enter the home, including crevices, wall cracks, windows, woodwork or floor gaps, cellar and outside doors and drains. Cockroaches need water to survive and thrive in high humidity, so make sure to fix and seal all leaky faucets and pipes. You may also want to have a trained exterminator go through the house when your family and pets are gone to eliminate any remaining roaches.

Roaches feel less welcome in a clean, dry house. To keep them from returning, keep food in tight-lidded containers and put pet food dishes away after they are done eating. Vacuum and sweep the floor after meals, and take out garbage and recyclables frequently. Use lidded garbage containers in the kitchen. Wash dishes immediately after use in hot, soapy water, and clean under stoves, refrigerators or toasters where loose crumbs can accumulate. Wipe off the stove top and clean other kitchen surfaces and cupboards regularly.

Indoor molds
Indoor molds and mildew thrive in areas of the house with increased humidity, such as damp basements and bathroom windows. These molds send out small spores that can trigger allergy symptoms.

Fortunately, indoor molds and mildew are easily eliminated once you discover them. Use a cleaning solution containing 5% bleach and a small amount of detergent. If mold or mildew are visible in carpeting or wallpaper, remove these items from the house. Also, promptly repair and seal leaking roofs or pipes. Never put carpeting on concrete or damp floors, and avoid storing clothes, papers or other items in damp areas.

Using dehumidifiers in damp basements may be helpful, but they generally cannot control humidity throughout the house. Empty the water in dehumidifiers and clean units regularly to prevent mildew from forming. All rooms, especially basements, bathrooms and kitchens, require ventilation and consistent cleaning to deter mold and mildew growth.

General consideration on indoor environmental control
Although you may be tempted to "air out" indoor allergens from the home, opening the windows can bring outdoor allergens such as pollen and mold spores into the house. Instead, use air conditioning to clean, recirculate and dehumidify the air in the home. You may also consider using in-home air filters, many of which can be used in conjunction with existing forced air cooling and heating systems. These include HEPA filtering systems; mechanical filters with standard disposable fiberglass filters that should be changed monthly; permanent air filters with baffles that should be cleaned periodically; and electrostatic filters that utilize the natural electrostatic properties of polypropylene and polyester to clean the air. The filters' plates should be cleaned frequently, or they may produce irritating ozone. Keep in mind that although air filters and devices may be popular, none have been scientifically proven to remove allergens and decrease allergy or asthma symptoms. Similarly, having air ducts cleaned, an expensive procedure, has not been shown to be effective in reducing respiratory symptoms. It is more effective to implement environmental control measures to reduce allergens.

Those with allergies and asthma should also avoid airborne irritants, including tobacco smoke, aerosols, paint, perfumes, cleaning products or other strong odors or fumes.

Indoor environmental control measures should focus on sites where allergens accumulate. By taking a thorough history and performing allergy tests, if needed, your allergist/immunologist can help you determine which indoor allergens provoke your symptoms. Environmental control measures differ for dust mites, animal allergens, cockroaches and molds. To relieve your symptoms, your allergist/immunologist may also prescribe appropriate medications, such as antihistamines, decongestants or asthma medications and allergy vaccine therapy.

Making changes to your indoor environment can take some time. To begin, you may want to write down a priority list. Progressive changes will produce an indoor environment that is less allergenic, easier to clean, and healthier for the whole family.