Air purifiers and humidifiers have different functions. Air purifiers are clean indoor air, but do nothing for indoor humidity levels. They remove dust and smoke from the air, as well as allergenic substances like animal dander and pollen. Humidifiers add water into the air, but do not clean it. They are used to relieve health issues from dry air and help reduce static electricity in the home. Mechanical air purifiers use filters to remove relatively large airborne pollutants, such as dust and pet dander, from the air. Filters are often made from foam, pleated paper or polyester, or some other synthetic material. A high efficiency particulate air filter, commonly known as HEPA, is capable of removing 99.97 percent of airborne particles. HEPA filters can remove extremely small particles, but cannot remove odors. An air purifier may combine a HEPA filter with a charcoal filter to help reduce odors. Humidifiers add water to indoor air, increasing the relative humidity of the indoor environment.

Dry winter air can cause chapped skin and contribute to respiratory problems. Adding moisture to the air with a humidifier can reduce dry skin and decrease breathing problems, including lessening coughs. Adding humidity to indoor air can also reduce static electricity and prevent wooden furniture from cracking. Four main types of humidifiers are ultrasonic, impeller-driven, evaporative and steam vaporizers. Ultrasonic and impeller humidifiers both produce a cool mist. Ultrasonic models are quiet because they use ultrasonic waves to produce mist, while impeller models use a rotating disk that can produce noise. Evaporative humidifiers use a fan to evaporate water into the air, and are also cold humidifiers. Steam vaporizers create a warm mist by heating water with an electrical element. Some models allow the mist to cool slightly before exiting the machine, and are known as warm mist humidifiers. The standing water in humidifiers can become home to a wide variety of bacteria, mold and fungi.

When the humidifier is turned on, these organisms can be released into your home’s air, and breathing them can cause lung problems and even infections. Best Laptop For Mechanical Engineering MajorIn the past, disinfectants used with humidifiers have also created problems. Moving A Shed MinnesotaMinerals from the humidifier’s water tank can be released into the air, where they settle out as a fine white dust. Blue Jean Curtain PanelsHumidifiers that use heat to evaporate water are prone to mineral build-up on the heating element, and the filters in evaporative humidifiers can also harbor bacteria and molds. You must keep humidifiers clean, and you need to occasionally descale them to remove mineral build-up. Gain 2 pounds per week

Gain 1.5 pounds per week Gain 1 pound per week Gain 0.5 pound per week Maintain my current weight Lose 0.5 pound per week Lose 1 pound per week Lose 1.5 pounds per week Lose 2 pounds per weekThe product: Dust, cigarette smoke, pollen and pet dander: With so many irritants floating around our homes and work places, clean air is a hot commodity. Americans spend hundreds of millions of dollars on furnace filters and air cleaners each year. Though some consumers are simply trying to bring a little extra freshness into their lives, many others hope that their investment will help relieve their asthma or allergies.If you've ever shopped for an air cleaner -- or if you've ever idly flipped through a SkyMall catalog -- you've undoubtedly seen ads for ionic air purifiers, devices that take an unusual approach to clearing the air. Instead of relying on fans to move air through filters, the machines release a steady stream of negatively charged ions that electrify the bits of dust, dander or other flotsam.

The airborne particles pick up the negative charge and become strongly attracted to positively charged collection plates inside the machine. (In many cases, they also become attracted to other charged surfaces such as walls, table tops and TV screens.) Except for a few models that use fans to help suck in the charged particles, most ionic air purifiers work silently. And, as ads are quick to point out, the devices generally don't have any motors or moving parts, and there are no filters to replace.There's another thing that separates ionic air purifiers from other technologies: To varying degrees, all ionic air purifiers release ozone, a potential pollutant. A 2006 study by researchers at UC Davis found that one popular brand, the Ionic Breeze Quadra, released about 2.2 milligrams of ozone per hour, or about as much as a constantly running photocopier. (Ionic purifiers shouldn't be confused with ozone generators that are marketed as "air cleaners." By design, these devices can release 50 to 200 milligrams of ozone per hour.)

Ionic purifiers are sold at drugstores, at department stores and via the Internet. The well-known and heavily advertised Ionic Breeze line is one of the cornerstone products of the Sharper Image, the high-end gadget store. One current offering, the Ionic Breeze GP, stands more than 2 feet tall and as an added feature comes equipped with a UV light to help kill airborne germs. If you buy one for $400, the second costs $200. The Sharper Image also sells a 13-inch unit for $150. You can buy a 28-inch Ionic Pro Turbo Air Purifier from Wal-Mart for $180. An online company called Heaven Fresh sells the table-top XJ-2000 ionic air purifier for about $50.The claims: According to the Sharper Image website, the Ionic Breeze is "proven effective at reducing airborne allergens and irritants -- with no fan, no motor and no noise." The Heaven Fresh website says that its purifiers can provide relief from "asthma, bronchitis, hay fever and other respiratory diseases." Heaven Fresh also claims that the ozone emitted by its machines helps clean the air.

According to the site, "ozone is one of the purest and most powerful oxidants and germicides known."The bottom line: Ionic air purifiers have undeniable appeal, but there's a problem: They don't really improve air quality, says Dr. James Sublett, a clinical professor at the University of Louisville; a fellow at the American College of Allergy, Asthma & Immunology; and co-chair of the 2007 ACAAI Healthy Indoor Environment conference. "We [allergists and immunologists] generally don't recommend them," he says. "This is a windmill that I've been tilting at for a number of years."According to Sublett, the devices don't effectively remove dust, dander and other irritants from a room. Without fans, he explains, they can't collect airborne particles from more than a few feet away. And when even small amounts of dust enter the device, the plates inside quickly lose much of their power to attract more particles. Meanwhile, the charged particles that stick to walls or TV screens haven't left the room and can always billow up again to cause trouble.

The ozone released from the devices is another deal-breaking shortcoming, Sublett says. "Ozone is a pollutant and an irritant. Even small amounts are too much." People who use several units at a time are especially likely to get an ozone overload, he says. One of Sublett's patients noticed a great improvement in her breathing when she turned off the six ionic purifiers in her home.The California Air Resources Board recently banned all devices that create an ozone concentration of more than 50 parts per billion, starting in 2009. Under normal conditions, ionic purifiers (as opposed to ozone generators) would fall below that threshold, says Jeffery Siegel, an assistant professor of civil, architectural and environmental engineering at the University of Texas at Austin who has studied the devices in laboratories as well as his own bedroom. Still, he says, the new standard is misleading because even products that release small amounts of ozone could easily reach that concentration in small, poorly ventilated spaces.