Reducing dust mite exposure

Townsend Letter for Doctors and Patients, Nov, 2005 by Jule Klotter

If a person is allergic to dust mites and shows signs of asthma, taking measures to control the mite population in the home can reduce respiratory problems and halt asthma progression. Dust mite avoidance is particularly helpful when signs of asthma first appear. In a rebuttal letter to a BMJ study by Gozsche et al. (1999: 318: 870 (27 March), SGM Cloosterman and OCP van Schayck say that peak flow rates and symptom scores of people with some early signs of asthma (but no diagnosis) stabilize when allergen concentration levels fall. People with mild asthma, however, show no clinical effect at a 6-week follow-up. The researchers believe that "allergen concentrations will need to be reduced for some time to reverse the already developed process of inflammation." Children with asthma and mite allergy particularly benefit from physical avoidance measures, according to TAE Platts-Mills et al. in the same BMJ issue.

The dust mite's fecal particles cause the allergic reaction, not the mite itself. The best way to reduce the amount of allergen in the home is to decrease the dust mite population. Dust mites thrive in high humidity with plenty of nesting areas (carpets, bedding, upholstered furniture, drapes). They feed on human skin scales, which explains why mattresses, pillows, and bedding provide an ideal environment for them. To prevent dust mite growth, indoor relative humidity should be below 50%. In dry climates, opening windows for an hour or so each day can reduce indoor humidity. In warm, humid areas, reducing humidity can be challenging, if not impossible--even with central air conditioning and basement humidifiers. Reducing nesting areas becomes all the more important. Replacing carpets with easy-to-clean linoleum or wood flooring and upholstered furniture with leather or vinyl seating will limit mite reproduction. Encasing pillows and mattresses with finely-woven coverings prevents mites from infiltrating these hard-to-clean items. Mite allergens in sheets and blankets can be controlled by washing the bedding every week or two. A cold water wash removes about 90% of the allergens. Killing the mites, however, requires hot water (131-140[degrees]F / 55-60[degrees]C). Because setting the water heater at such a high temperature creates a safety hazard for children, other measures may be used instead. The old-time practice of exposing rugs, pillows, and bedding to at least three hours of strong sunlight kills mites. For smaller objects, like soft toys or clothing, 20 minutes or longer in a dryer at full temperature or freezing them in the kitchen freezer will also do the trick. Dr. Thomas Platts-Mills says that by reducing or avoiding exposure, people "can gain control of their illness, reduce symptoms and in many cases they can reduce reliance on pharmaceutical products." Scientific studies have also identified cats and cockroaches as other allergens that affect the progression of asthma in the allergic.

Cloosterman, SGM; van Schayck OCP. Effectiveness of measures depends on stage of asthma (letter) BMJ 1999;318:870 (27 March) (accessed 9 August 2005)

Platts-Mills TAE. Allergen Avoidance. www.worldallergy.org (accessed 11 August 2005)

Platts-Mills TAE; Chapman MD; Wheatley LM. Conclusions of meta-analysis are wrong. BMJ 1999;318:870 (27 March) (accessed 9 August 2005)