Does house dust mite aggravate atopic eczema?

Abstract

The significance of reports1,2, that topical application of house dust mite (HDM) to abraded or excoriated uninvolved skin of patients with atopic eczema can provoke an eczema‐like reaction is controversial. We have therefore studied 17 adult in‐patients with atopic eczema who demonstrated positive prick tests to Bencard HDM solution. One ml of Bencard HDM solution was applied, under a crepe bandage, daily for 5 days to an untreated 10 cm2 mildly eczematous area behind one knee, and diluent only, similarly, to the other knee in a double‐blind fashion. Test sites were assessed daily for itch using a visual analogue scale and for severity of erythema, papules and excoriation using a 3‐point grading system. Comparing these parameters between active and control sites for each patient, local worsening of eczema in response to HDM was marked in 5/17, moderate in 3/17 and mild in 4/17 subjects, while mild deterioration with diluent only occurred in 3/17. Mean area of active eczema increased by 6 26 ± 8 4 cm2 (± SD) at HDM‐treated and by 0 5 ±1.5 cm2 at control sites (P≤0.01; paired t‐test). Further patients exposed to Bencard horse hair extract, to which they were prick‐test negative, in place of HDM, showed no reaction. These results indicate that HDM can exacerbate pre‐existing atopic eczema.