Preventive measures in house-dust allergy.

To evaluate the effect of preventive measures on the concentration of house-dust mites (Pyroglyphidae), the homes of 23 consecutive patients allergic to house-dust mites and the homes of 75 randomly selected control subjects were studied. Although the patients' homes were cleaned more frequently (p less than 0.0007 for 4 cleaning qualities), greater concentrations of house-dust mites (p = 0.0073) were found in dust from bedroom carpets in the patients' homes than in the homes of the control subjects. A tendency (p less than 0.15) in the same direction was found for mattress surfaces and living room carpets. High absolute humidity of indoor air was related to greater concentrations of house-dust mites. There was a tendency (p less than 0.10) towards higher humidity in the patients' homes than in those of the control subjects. It was concluded that high humidity improves the survival of house-dust mites in homes. Energy saving measures such as installing insulation raises indoor humidity and can lead to an increased incidence and severity of house-dust mite allergy.