Abstract: We included seven studies of 324 adults and children with eczema. Overall, the included studies had a high risk of bias. Four of the seven trials tested interventions with multiple components, and three tested a single intervention. Two of the seven trials included only children, four included children and adults, and one included only adults. Interventions to reduce or avoid exposure to house dust mite included covers for mattresses and bedding, increased or high-quality vacuuming of carpets and mattresses, and sprays that kill house dust mites. Four studies assessed our first primary outcome of 'Clinician-assessed eczema severity using a named scale'. Of these, one study (n = 20) did not show any significant short-term benefit from allergen impermeable polyurethane mattress encasings and acaricide spray versus allergen permeable cotton mattress encasings and placebo acaricide spray. One study (n = 60) found a modest statistically significant benefit in the Six Area, Six Sign Atopic Dermatitis (SASSAD) scale over six months (mean difference of 4.2 (95% confidence interval 1.7 to 6.7), P = 0.008) in favour of a mite impermeable bedding system combined with benzyltannate spray and high-filtration vacuuming versus mite permeable cotton encasings, water with a trace of alcohol spray, and a low-filtration vacuum cleaner. The third study (n = 41) did not compare the change in severity of eczema between the two treatment groups. The fourth study (n = 86) reported no evidence of a difference between the treatment groups. With regard to the secondary outcomes 'Participant- or caregiver-assessed global eczema severity score' and the 'Amount and frequency of topical treatment required', one study (n = 20) assessed these outcomes with similar results being reported for these outcomes in both groups. Four studies (n = 159) assessed 'Sensitivity to house dust mite allergen using a marker'; there was no clear evidence of a difference in sensitivity levels reported between treatments in any of the four trials. None of the seven included studies assessed our second primary outcome 'Participant- or caregiver-assessed eczema-related quality of life using a named instrument' or the secondary outcome of 'Adverse effects'. We were unable to combine any of our results because of variability in the interventions and paucity of data. We were unable to determine clear implications to inform clinical practice from the very low-quality evidence currently available. The modest treatment responses reported were in people with atopic eczema, specifically with sensitivity to one or more aeroallergens. Thus, their use in the eczema population as a whole is unknown. High-quality long-term trials of single, easy-to-administer house dust mite reduction or avoidance measures are worth pursuing.

Plain-language summary: We found seven randomised controlled trials, which included 324 adults and children with eczema. We conducted the search up to 14 August 2014. Two of the seven trials included only children; four included children and adults; and one only included adults. Four of the seven trials compared treatments made up of multiple different house dust mite reduction and avoidance measures, and three trials tested a single treatment. The treatments were compared against other house dust mite reduction or avoidance treatments, no treatment, a placebo intervention (e.g., cotton bed covers), or standard care only. We did not find any evidence to inform clinical practice. Some small treatment responses reported were in people with atopic eczema who were sensitive to one or more airborne allergens. We found no evidence of benefit in the other six included studies. Therefore, their use in the eczema population as a whole is unknown. High-quality longer trials of single, easy-to-use house dust mite reduction or avoidance measures should be performed. These seven very low-quality (Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach) small trials do not provide enough evidence to recommend any of the house dust mite reduction and avoidance measures tested.