Permeability of synthetic and feather pillows to live house dust mites and house dust R. Siebers*, H.-S. Namw and J. Crane* *Wellington Asthma Research Group, Wellington School of Medicine and Health Sciences, Wellington, New Zealand and wGenome Research Center for Allergy and Respiratory Diseases, Soonchunhyang University, Bucheon, Republic of Korea Summary Background Previous studies have demonstrated significantly higher house dust mite (HDM) allergen levels from synthetic pillows, compared to feather pillows. Reasons for these differences could be lower permeability of feather pillow coverings to allergen in dust, greater HDM penetration of synthetic pillow covering, or both. Objectives To determine the permeability of synthetic and feather pillow coverings to live HDMs and house dust. Methods Twenty live adult HDMs were seeded on top of two types of synthetic pillow covering (one standard polyester and one newer polyester/cotton type) and one type of feather pillow coverings with adequate food supply below in sealed culture dishes, kept at 23 1C and 70% relative humidity. After 24 and 48h live HDM numbers remaining on top of the coverings were enumerated microscopically. Three aliquots of fine house dust (each in triplicate) were placed on top of the synthetic and feather pillow coverings, shaken gently for 30min and penetrated dust was collected and weighed. Results After 24h, all 20 HDMs had penetrated the standard synthetic pillow coverings, and no HDMs had penetrated either the feather pillow or the new synthetic pillow coverings after 24 or 48 h. Dust permeability (% of applied dust) for the standard synthetic, new type synthetic and feather pillow coverings were 0.88%, 0.07%, and 0.07%, respectively. This compared to 0.02% for a commercial occlusive pillow cover. Conclusions These findings of total permeability of standard synthetic pillow coverings to live HDMs, and their greater permeability to house dust could explain their reported higher HDM allergen levels, compared to feather pillow coverings. Newer types of synthetic pillow coverings are similar to feather pillow coverings in their permeability to live HDMs and house dust. Keywords allergens, feather, house dust mites, permeability, pillows, synthetic Submitted 31 July 2003; revised 16 October 2003; accepted 29 February 2004 Introduction Synthetic bedding materials are associated with increased asthma symptoms in sensitized subjects [1]. Recently, a prospective longitudinal birth-cohort study has shown that use of feather bedding was negatively associated with bronchial obstruction, asthma, and allergic rhinitis in child- hood [2]. A plausible explanation for these findings could be the previously reported differences in house dust mite (HDM) allergens of different bedding materials, as sensitization to allergens is a known risk factor for the development of asthma in susceptible subjects. Studies in New Zealand and the UK have consistently demonstrated significantly higher HDM allergens from synthetic pillows than from feather pillows [3–5], and also from other synthetic bedding materials [6]. Differences have also been demonstrated for cat and dog allergens [7]. The reason for higher HDM allergen levels on synthetic bedding is, as yet, not known. We have previously noted that the weave of feather pillow coverings is much tighter than synthetic pillow coverings (figure in ref. [1]). This potentially could block live HDM penetrating the pillow covering, or could minimize allergen passage, compared to synthetic pillow covering. We, therefore, studied the permeability of synthetic and feather pillow coverings to HDM and house dust as a potential explanation for the previously reported findings of higher HDM allergen levels on synthetic bedding materials [3–6]. We also studied a newer type of synthetic pillow covering, introduced commercially in New Zealand in response to our Editorial in Clinical and Experimental Allergy urging bedding manufacturers to produce synthetic bedding coverings with a tighter weave than currently used [8]. Correspondence: Robert Siebers, Wellington Asthma Research Group, Wellington School of Medicine and Health Sciences, PO Box 7343, Wellington South, Wellington, New Zealand. E-mail: rob@wnmeds.ac.nz Clin Exp Allergy 2004; 34:888–890 doi:10.1111/j.1365-2222.2004.01972.x r 2004 Blackwell Publishing Ltd 888