Most people with allergies or asthma know well the hazards of dust mites, the microscopic household critters long said to be one of the most common triggers of allergic symptoms.

But that is not what studies show. Scientists have repeatedly found that various physical and chemical methods recommended for controlling dust mites, like sprays and impermeable bed covers, do little by themselves to prevent allergies. If they do work, it is usually as one of several steps taken to reduce household allergens.

An analysis published in 2008, for example, looked at 54 randomized studies that compared various mite-control measures with placebo interventions, or none at all, in people with asthma. It found that the control measures made no significant difference. A 2007 study followed 126 asthma patients, some of whom were trained to use control measures like impermeable bed covers and others who used placebo interventions.

After two years, the scientists found that the groups showed no difference in their use of inhalers or reductions in symptoms like wheezing and coughing.

These and other studies suggest that people with allergies and asthma would do well to rely on a broad programme of interventions, like frequently washing clothes and blankets, using air conditioning instead of humidifiers, and strictly limiting exposure to allergens like smoke and strong odours.

The verdict:

Research suggests that controlling dust mites alone may not prevent allergies.

NYT