Background The role of housedust-mite (HDM) allergen (Der p1) in the pathogenesis of atopic dermatitis is controversial. We tested the hypothesis that atopic dermatitis improves if amounts of HDM allergen in the home are reduced.

Methods Active treatment comprised Goretex bedcovers (placebo, cotton covers), benzyltannate spray (placebo, water), and a high-filtration vacuum cleaner (placebo, a conventional domestic vacuum cleaner). Dust was sampled monthly from the mattress covers and bedroom and living-room carpets. 48 patients (24 adults [mean age 30] and 24 children [mean age 10]) completed the 6-month study. 28 were in the active treatment group and 20 in the placebo group.

Findings The weight of dust collected from Goretex-covered mattresses had fallen by 98% at 1 month (from 386 to 9 mg/m²) with no change thereafter. Placebo covers caused a smaller reduction in dust load (361 to 269 mg/m²); the difference between active and placebo covers at 6 months was highly significant (p=0·002). Both active and placebo treatments caused significant reductions in Der p1 concentrations in bedroom and living-room carpets and the differences between the treatments were not significant. The severity of eczema decreased in both groups, but the active group showed significantly greater improvements in severity score (difference between mean final scores 4·3 units, p=0·006) and area affected (difference between mean final areas 10%, p=0·006) in analysis of covariance with initial mattress dust weights and bedroom carpet Der p1 load as covariates. Reported analysis with final values for the covariates showed that most of the treatment effect was due to the reduction in mattress dust and carpet Der p1.

Interpretation The activity of atopic dermatitis can be greatly reduced by effective HDM avoidance. Methods to identify individuals who will benefit most from such measures are needed.