Letters

Increased house dust mite allergen in synthetic pillows may explain increased wheezing

We have shown that synthetic pillows have eightfold higher amounts of Der p I than feather pillows.² Peat et al and Custovic et al have shown a clear dose-response relation between amounts of Der p I in the home and current asthma symptoms.^{3 4} Therefore an eightfold variation in total Der p I in an allergen reservoir on which people rest the access to their airways every night might be relevant.

We have subsequently examined the accumulation of Der p I in new synthetic and feather pillows and confirmed our previous findings. We placed a pair of new synthetic and feather pillows on the same beds in 12 homes. After four months the synthetic pillows yielded a geometric mean concentration of 7.03 µg Der p I/g fine dust (95% confidence interval 3.41 to 14.49) and feather pillows 1.09 µg Der p I/g (0.15 to 2.18) (P=0.0001). Corresponding values at the start of the study were 1.83 µg/g (0.15 to 4.88) for synthetic pillows and 0.67 µg/g (0.36 to 1.60) for feather pillows.

The increased exposure to house dust mite allergen from synthetic pillows may explain the increased asthma symptoms. However, there remains the possibility that part of the reason lies in bias associated either with a switch to synthetic pillows by parents of asthmatic children or with parents of asthmatic children always having used synthetic pillows for their asthmatic child. In trying to reduce this bias Strachan and Carey may not have excluded children by asking parents if they had made "alterations to the child's bedroom ...."

Julian Crane, Professorial research fellow,^a Trudi Kemp, Senior research fellow,^a Robert Siebers, Senior technical officer,^a Natalie Rains, Research assistant,^a David Fishwick, Senior research fellow,^a Penny Fitzharris, Clinical allergist ^a

^a Wellington Asthma Research Group, Wellington School of Medicine, Wellington, New Zealand

1. Strachan D, Carey I. Reduced risk of wheezing in children using feather pillows is confirmed. BMJ 1997;314:518. (15 February.) [Free Full Text]
2. Kemp T, Siebers R, Fishwick D, O'Grady G, Fitzharris P, Crane J. House dust mite allergen in pillows. BMJ 1996;313:916. [Free Full Text]
3. Custovic A, Taggart S, Francis H, Chapman M, Woodcock A. Exposure to house dust mite allergens and the clinical activity of asthma. J Allergy Clin Immunol 1996;98:64-72. [Medline]
4. Peat JK, Tovey E, Toelle BG, Haby MM, Gray EJ, Mahmic A, et al. House dust mite allergens. A major risk factor for childhood asthma in Australia. Am J Respir Crit Care Med 1996;153:141-6.