If you have asthma, it’s important to avoid asthma triggers whenever possible -- but sometimes it’s not so easy. A reader asks: I am meticulous about keeping my home dust free, but it doesn't seem to help my asthma. Am I doing something wrong?

A. Probably not, according to a recent review of studies of house dust-mite control measures for asthma reported in the Cochrane Database of Systematic Reviews. The review of 54 studies found no effect of chemical or physical methods aimed at reducing exposure to house dust-mite allergens. The total number of asthma patients who improved after some type of allergen treatment was very similar to the number in the control groups who did not try to mite proof their homes.

This finding is surprising, considering that environmental control of allergens, such as chemical treatments, mattress covers, vacuum cleaning, washing, or air filtration, is usually recommended for people with asthma. In fact, recent U.S. guidelines, which recommend a host of tips for limiting allergens in the home, include dust-mite control measures among their recommendations. But the review authors dismiss some of the studies used to formulate the guidelines as inadequate.

If you have asthma and find that it's improved since you have taken steps to mite proof your home, don't stop. But if these methods don't seem to help you, ask your doctor if there are other ways to improve your breathing, including changing your drug treatment.