A: Dan, it’s good that you’re thinking about ways to help reduce your own and your son’s allergies and asthma. The air quality in your home is very important since that is where you and your family spend most of your time.

Air cleaning machines can remove some particles from the air that can cause allergies and asthma, e.g., dust, smoke particles, pollen, mold and animal dander. But they don’t remove particles that have settled on surfaces, nor do they remove viruses or gases such as carbon monoxide, which can also cause asthma attacks. Some studies have found that air cleaners can make small improvements in allergy and asthma symptoms; but other studies have not found that they make any difference.

Air cleaners come in different sizes. Room air cleaners are portable machines that can be placed in an individual room (e.g., your child’s bedroom) and range in price from $100 to $500. Central air cleaners are professionally installed systems that work within a forced-air heating and cooling system in your home, ranging in cost from $350 to $1,200 plus installation costs.

Air cleaners are rated according to their effectiveness, which depends on the airflow rate and how efficiently they remove particles of different sizes. Air cleaners work by either filtering the air to trap particles (e.g., a HEPA or high-efficiency particulate arresting filter), or by using an electrically charged plate to trap particles (e.g., electrostatic precipitators or negative ion generators). Health experts have warned, however, that the electrical air cleaners can produce ozone, which can trigger asthma attacks in some people.

Whether or not you get an air cleaner, health experts agree that the best way to reduce allergy and asthma symptoms is by doing everything you can to prevent indoor air pollution:

1. Don’t allow smoking in your home.

2. Don’t use a wood stove, fireplace or kerosene heater.

3. Ensure good ventilation. Open windows and doors in good weather; and use the air conditioner during pollen season. Make sure your stove, clothes dryer and bathroom are well vented to the outdoors: use the vent fan when cooking and the bathroom vent fan after showers.

4. Have your furnace inspected and cleaned regularly.

5. Use sturdy doormats at entrances to your home. Consider having people remove their shoes when entering your home.

6. Keep carpets and floors clean. Wet mop floors. Consider replacing carpets with area rugs that can be cleaned more easily. And consider getting a vacuum with a HEPA filter.

7. For dust mite allergies, use impermeable covers on mattresses.

8. If a family member has pet allergies, it’s best not to have a furry pet.

9. Don’t use “air freshener” sprays, scented candles, incense, potpourri, mothballs, spray furniture polish, toilet deodorizers, hairspray or insecticide sprays. These release chemicals that can contribute to asthma.

For more information on air cleaning machines, visit the U.S. Environmental Protection Agency website www.epa.gov/iaq/pubs/residair.html.