In most homes, the largest population of dust mites is in the bedroom, especially in mattresses, pillows and carpeting.

When your grandchildren lay down to sleep, they are pressing their noses against some of the most popular gathering places for mites. Reducing exposure to mites in their bedrooms, and especially their beds, can be the most powerful way to fight dust mite allergy. Here's how:

• Wash mattress pads, comforters and blankets in hot water every seven to 10 days.
• Cover mattresses, box springs, and pillows in allergen-proof encasements. Mites and their debris can't pass through because these covers are made with tightly woven material. Studies have not shown great benefit from these products, but many experts believe that these covers may be worth their modest cost.
• Keep a bedspread on your bed all day to collect dust, but carefully remove it from your bedroom (without shaking it!) before you go to sleep.
• Avoid feather or down pillows.
Instead, use washable pillows that can stand a hot water wash (polyester fiber-fill such as Hollofil or Dacron).
• Don't use fuzzy blankets unless they can be regularly washed.

They tend to collect more dust than blankets with a thin weave. Other dust collectors include stuffed animals, wall-to-wall carpeting, rugs that are not easily washable, and bed canopies. These items should be removed from the bedroom or avoided.

Air cleaners and air filters that remove dust are a costly solution that may not be worth the investment. No air cleaners work well enough to substitute for other steps you can take to cut down on indoor allergens. Air cleaners that generate ozone gas have no effect on allergens in the air. And they may worsen allergy symptoms because the ozone they emit can irritate the respiratory system.

Some people try to reduce dust mite allergy by treating places where dust mites gather (like carpets and furniture) with sprays containing tannic acid. Tannic acid chemically changes the protein that is the source of dust mite allergy so it can no longer act as an allergy trigger. This treatment is not very practical because it is difficult to use it frequently enough to provide a noticeable benefit. Tannic acid must be regularly reapplied because it does not kill mites, and mites will quickly produce new feces. In general, I do not recommend the use of tannic acid. There are better ways to control dust mites.

Poisoning dust mites once every six months with benzyl benzoate (Acarosan), which comes in dry foam carpet and furniture cleaners, may help if you can't remove rugs.

Spray products such as tannic acid and benzyl benzoate can stain some carpets.