Air filters ranges from small, inexpensive desktop models to whole house air conditioning systems. Some do you a lot more good than others. Some, in fact, are worthless. The ones that work are a real blessing, though. ”I almost always prescribe air filtration,” says Dr. Boxer. ”I feel it's helpful. I’ve seen asthma patients who were helped immensely by just using an air filter.”

”Air filtration is certainly a very natural way of controlling symptoms,” says Dr. Falliers. ”There are dozens of products, and each has to be examined for what is does and doesn’t do.” Air filters may be installed in the ductwork of either your warm air furnace or air conditioning system. Or you can buy portable models tat sit anywhere in the room. Or even hook up to the cigarette lighter in your car. Portable units can sometimes be rented.

Activated charcoal filters. The odor eating capacity of activated charcoal varies with the humidity and temperature of the air in the room, the concentration of fumes and the type of odors in the air. Guy O. Pfeiffer, M.D., of Mattoon, Illinois, studied activated charcoal filters and found that they're generally pretty good for absorbing cooking and food odors (even from burned dinners and foods such as garlic, onions, cheese and citrus); cigarette and tobacco odors; diesel and gasoline fumes; smog and ozone; and the odors from pets, mothballs and perfume.

Charcoal is slightly less powerful against pollen, coal smoke, mildew, chlorine, fish odors and some noxious gases. And it's useless against carbon monoxide and formaldehyde. Installed piggyback with another type of filter, however, charcoal can be helpful; one catches what the other misses.

Electronic air cleaners. The most common type of electronic air cleaner is the electronic precipitator. Until a few years a go, electronic air cleaners were standard equipment for eating asthma and respiratory allergy. They act much like an electromagnet for air pollution: a fan draws in particles, zap them with an electric charge and collects them on a plate.

The charged particles are supposedly taken out of circulation. However, J. Gordon King, a consultant in air contamination, writes that although electrostatic precipitators are popularly advertised as being 95 to 99 percent efficient, they're not. In reality , says Mr. King, electrostatic air cleaner available for home use rarely trap more than 80 percent of the particles in the air.

What’s worse, efficiency can drop to as low as 20 percent within a short period of time – especially for bigger particles like pollen (Respiratory Care, March – April, 1973). That means electrostatic air cleaners are no more effectively than putting a sheet of gauze over your mouth.

And the charged particles that escape the filters build up on walls and furniture faster than if no cleaner was used at all. To top it all off, all electronic air cleaners produce ozone, a highly toxic gas which causes headache in some people. So you may not want to bother with them at all.

HEPA (High Efficiency Particulate Air) Filters. These filters work a lot better than electronic air cleaners. Air that’s been cleared by a HEPA is free on 99.97 percent of all contaminating particles, according to the National Bureau of Standards. That’s about as clean as you can get in today’s environment.

And they maintain their efficiency throughout their operating life of two to five years. HEPA filters work well against pollens, molds, yeast and other fungi, bacteria and viruses – a boon to allergy sufferers prone to the frequent colds and flu attacks.

HEPA filters have been known to relieve hay fever and asthma symptoms within ten minutes to half an hour. When potassium permanganate or activated charcoal is added, an HEPA filters can clear the air of jumbo particles like dust and pollen as well as minute chemical odors.

HEPA units with metal casings are better for chemically sensitive people than units with casings made of pressboard (which contains formaldehyde) or plastic.

HEPA filters did wonders for reducing nightly asthma attacks for asthmatic, children at a summer camp in West Virginia, according to the camp’s medical director Merle S. Scherr, M.D. in his report, Dr. Scherr emphasized that HEPA units are an important part of treatment of allergic asthma (West Virginia Medical Journal, July, 1977).

HEPA units are also a godsend for preventing nightly asthma attacks for asthmatic children at home in winter. Normally, cold nights require furnaces to work harder, so furnace fans circulate more dust- and trigger more asthma. But when HEPA filters were tested on 18 children with hard to control asthma, the children collectively logged 140 nights of disturbed sleep with use of the filter, as compared to only 45 peaceful nights without the filter.

”This... not only relieved the parents of having to get up in the night and care for these children,” say the researchers who conducted the study, ”but we feel that the child, if well rested, felt better, performed better during the day and was probably more resistant to illness.” Several if the children were also able to cut down on their asthma medicine, and they no longer missed any school (Annals of Allergy, June, 1973).

Air conditioning. Pollens counts in a closed, air conditioned room plummet to around zero. In an unfiltered room, with the window open, pollen levels are about one third the outdoor level – enough to aggravate symptoms in everyone with pollen energy. So air conditioners or central, whole house systems are better at filtering out pollen is not exactly clear.

In general, pollen and mold levels tend to run lower in houses with air conditioning of any kind than in houses with no air conditioning whatsoever, largely because the doors and windows are closed. Whether you go in for a whole house system or individual window units simply depends on what you can afford.

Backed up by separate HEPA unit, air conditioning of any type is optimized. Be sure to clean the coils and filters, however, to prevent mold contamination. And don’t run the air conditioner too high: too cold air can aggravate respiratory allergy.

Note: When prescribed by a doctor, an air filter is a tax deductible medical expense. So is the cost of installing air conditioning equipment, minus the amount by which it raises the value of your property. For example, if you spend $1,200, you can legitimately deduct $800.

Negative ion generators. These gizmos generate negatively charged air particles (ions) – which are theoretically good for us – and thus replace positively charged ions – which are supposedly bad for us. Scientists haven’t exactly rushed to support the health claims made for negative ion generators. But if you’re allergic to particles such as dust, pollen or smoke, you may derive some benefit from their use.

That’s because negative ions travel around the room scavenging larger contaminants, which are then electro-statically attracted to walls, carpets, draperies, furniture and other surfaces closer to the ground – and away from our breathing space. Some do better job of cleaning than others, however. The units equipped with a disposable collection pad are probably somewhat better.

Dr. Falliers describes negative ion generators this way: ”In current scientific studies in which one group of asthmatics used a negative ion generator and another used a machine that did nothing, there was no significant difference in their symptoms. Yet individual cases of improvement are so impressive that I certainly would like to give anybody the benefits of trying one.”

Miscellaneous ”tabletop” Air Purifiers. You may have noticed small portable fan and filters units – marketed as purifiers – in the house wares department of your neighborhood department store or advertised on TV. About the size of a desk telephone, these appliances come in all shapes and colors. Most feature a small, electrically driven fan which draws air through a filter.

Some contain activated charcoal or chemicals to absorb odors and contaminants. They sometimes claim to control formaldehyde. We wish we could recommend these devices, but not much has been done study their ability to clean the air. Considering their small size and the big job they're supposed to do, researches say you’d probably be better off with an HEPA filters on air conditioning.

Every little bit helps

We’ll be the first to admit that a pristine pure environment – completely devoid of dust, pollen or chemicals – is unattainable. You can, however, realistically reduce your exposure to a variety of the most troublesome items. Start small, eliminating one source at a time. You should soon find yourself feeling better. ”Allergy is reversible disease,” says Dr. McGovern. ”if you give your immune system a chance, it will heal every time.”