Indoor air pollution is a serious problem. According to the Environmental Protection Agency (EPA), air pollution levels are two to five times higher indoors. In some buildings with a lack of proper ventilation, the indoor air may be 100 times more polluted than the air outside! This is because modern buildings are constructed with energy efficiency in mind. However, the tight seals that make a home energy-efficient also trap pollutants inside. On top of that, the average American takes nine out of ten breaths indoors, so it's imperative to make sure that your indoor air is free of allergens and other impurities.

Air purifiers eliminate allergens, toxic chemicals, and other dangerous pollutants. This article explains why people use air purifiers, how they work, which air purifiers you should avoid, and how to select the best air purifier for your needs.

Common Indoor Air Pollutants

What is the source of indoor air pollution? In terms of organic pollutants, mold and dust mites are everywhere - and they are the two most common causes of year-round allergic rhinitis (hay fever). Pollen is also a pervasive allergen that always finds its way into your home since it is so small and sticky. If you have pets, they will surely spread their dander to every nook and cranny of your home. Many viruses and bacteria are also airborne.

Even though they are not organic allergens, Volatile Organic Compounds (VOCs) cause many people to experience allergic reactions and other health problems. VOCs include formaldehyde, fragrances, pesticides, solvents, and cleaning agents. VOCs can enter the air through chemical off-gassing from furniture, new carpets, adhesives, plastics, and various building materials. Furthermore, many VOCs are known carcinogens (cancer-causing agents).

Environmental contaminants like cigarette smoke, carbon dioxide, carbon monoxide, and nitrogen dioxide may also be present in your indoor air, as well as toxic heavy metals like airborne lead, mercury vapor, and radon.

How Air Purifiers Work

HEPA air purifiers use a HEPA air filter, which was developed by the Atomic Energy Commission in the 1940s as a way to filter radioactive contaminants. HEPA filters set the standard for air purifiers: to be classified as HEPA, a filter must capture a minimum of 99.97% of pollutants at 0.3 microns or larger. Top-selling HEPA air purifiers include the Austin Air purifier, available with a HEGA (High Efficiency Gas Adsoprtion) filter, along with air purifiers from IQAir, Allerair, Blueair, and Honeywell.

Activated carbon filters remove gases, odors, and chemical toxins. The carbon is "activated" when it is treated with oxygen, which opens up millions of tiny pores to attract and adsorb chemicals. Impregnated carbon filters have been treated with an additional chemical, normally either potassium iodide or potassium permanganate; these chemicals, known as chemisorbents, improve the carbon filter's ability to trap VOCs and other chemically reactive gases.

Electrostatic filters use an electrostatic charge to attract pollutants and trap them on collector plates. These filters are great for people who don't want to have to worry about changing HEPA filters, but if the collection plates are not cleaned frequently, they quickly lose efficiency. Also, beware that some electrostatic filters emit ozone, which is known to be a powerful lung irritant and can be very irritating to some people with asthma or allergies. The Friedrich air purifier is, by far, the best electrostatic air purifier, as well as the overall top-ranked air purifier in previous Consumer Reports rankings

Charged media filters give pollutants an electrostatic charge before collecting them in a traditional filter. Charged media filters are typically quite effective, but like electrostatic filters, they lose efficiency rapidly?and they may require frequent and expensive filter changes. Some charged media air filter units also emit ozone. The advantage of charged media filters is that they are quieter and more energy-efficient than HEPA air purifiers. The Blueair air purifier is the best charged media filter, and it does not emit ozone.

Where and How to Use an Air Purifier

If you suffer from allergies (especially if you're allergic to dust mite allergen), then the best place for an air purifier is your bedroom. It's essential to have clean air in your bedroom because you spend about a third of your life there. If you're allergic to animal dander and have pets, then you may want to place an air purifier in the room where your pets spend most of their time?and keep the pets out of your bedroom! Also, you should not place an air purifier in the corner of a room; it should be at least a couple of feet away from the walls for maximum air flow.

You should run your air purifier continuously for optimum performance. Most air purifiers have high and low settings. Even if you go on vacation, we recommend that you keep your air purifier running on low. Otherwise, you'll return to a house full of polluted air! If you are concerned about your electric bill, find out how much energy an air purifier uses before buying it. Typical HEPA air purifiers can use anywhere from 50 watts on low to 200 watts on high. For comparison, a typical lamp uses about 60 watts, while a typical computer uses about 365 watts.

Air Purifiers to Avoid

Avoid ozone generators and ionizing air cleaners. These air purifiers create ions that attract pollutants; however, many of the pollutants are released back into the air, often times leading to dirty spots on nearby walls. Besides the fact that they don't do a good job of cleaning the air, ozone generators and ionizing cleaners also emit ozone. Ozone, a main component of smog, could potentially lead to a serious asthma attack.

Moreover, David Peden, researcher at the Center of Environmental Medicine and Lung Biology at the University of North Carolina, has examined how ozone exposure might exacerbate the allergic response of people who are allergic to dust mites, and his results suggest that ozone worsens the asthmatic response. The EPA has warned consumers against using ozone generators, and Consumer Reports recommends against the newest Ionic Breeze Quadra, despite the addition of OzoneGuard, a device meant to eliminate some of the dangerous ozone emitted by the Ionic Breeze.

Consumer Reports points out: "Our air-cleaning tests show that the Ionic Breeze with OzoneGuard does a poor job of removing smoke, dust and pollen particles from the air when new and after 500 hours of continuous use" and "the Ionic Breeze with OzoneGuard still adds ozone to the air."

How to Buy the Best Air Purifier

The air purifier market is vast and riddled with confusing and often misleading advertising schemes. If you're shopping for an air purifier, then you should first consider what kind of pollutants you're trying to eliminate. For example, if you have problems with cigarette smoke, then you'll want to make sure your air purifier has the ability to eliminate fumes, VOCs, and other gases. You may also want to consider the following factors before buying an air purifier: the area coverage (make sure the square footage listed for the air purifier is about the same or slightly greater than the square footage of the room where you intend to use it); the ACH rating (Air Changes Per Hour?this number lets you know how frequently the air purifier can exchange all the air in a given room); the CADR (the Clean Air Delivery Rate tells you how much air is purified and how well it is purified); the price; how often you have to replace the filters and how much they cost; the noise level of the air purifier; energy usage; whether it emits ozone; extra features (like a filter change indicator light); the manufacturer's reputation; and the warranty.

Visit achooallergy.com to learn more and browse a large selection of top brand air purifiers.