A randomized trial of dehumidification in the control of house dust mite

Background House dust mites (HDM) are sensitive to humidity. Few studies ha ve adequately examined the potential of dehumidification in reducing HDM nu mbers. Objective The study examined the effect of portable domestic dehumidifiers, and a behavioural programme to reduce humidity, on HDM counts and HDM alle rgen levels. Methods A randomized controlled trial was undertaken. A total of 76 homes w ere allocated to three groups that received a portable domestic dehumidifie r, a behavioural programme, or no intervention. Humidity, temperature, HDM counts (trap and vacuum samples), HDM allergen, and other details of the ho me environment were measured on four occasions over a period of 1 year. Int erventions and measurements were concerned predominantly with one bedroom. Results There was a reduction in relative humidity in the dehumidifier grou p, but not the behavioural group. A decline in HDM trap counts was observed for all three groups. Change scores did not indicate that the dehumidifier group had a greater decline than the other groups. A secondary analysis ex amining presence or absence of HDM showed a shift from households having HD M at baseline to households not having HDM in the final round for some trap measures. Change score analysis indicated that this shift was greater in t he dehumidifier group compared with other groups. The dehumidifier group di d not show a greater decline in HDM allergen than that seen in the other tw o groups. Conclusion Neither the dehumidifier nor the behavioural intervention had a major effect on HDM counts or allergen levels. However, the study did have a number of limitations relating to size, timing of intervention, and runni ng of the dehumidifiers. The secondary data analysis may indicate some effe ct of dehumidification, but clearly this effect was small. There is a need for more information on the effects of reducing ambient humidity on the dis tribution of HDM within their habitats.