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Lie-ins keep bed clear of mites

November 19, 2004 By Mark Peplow This article courtesy of Nature News.

Dust-mite racetrack reveals preference for cool habitats.

Dust mites are not renowned for their sprinting ability. But now they have their very own racetrack, courtesy of scientists who are studying mite behaviour. According to these specialists, staying in bed longer is a good way to keep your sheets mite-free.

House dust mites (Dermatophagoides pteronyssinus) are thought to be a major cause of asthma and other allergic reactions, which are increasing across the world. People who are allergic react to proteins in the bodies and faeces of the mites. Because the mites feed on scales of dead human skin, they are often found sharing our beds.

"The idea of the track is to study how mites move and how they are affected by changes in temperature and humidity," says Marcella Ucci, a built-environment expert at University College London, who works on the dust-mite project. The scientists hope their research will help homeowners to deal with the creatures, which are less than a millimetre long.

Chemical sprays are available to kill the mites, but the creatures can evolve resistance extremely quickly. "And people are reluctant to spray insecticides on their beds," adds Ucci's colleague Toby Wilkinson, who is a consultant for Insect Research and Development, a company based in Hertfordshire. "This is a purer approach because we're trying to stop the mites developing there in the first place," he says.

The tiny races have helped the researchers model how changes in the domestic environment can reduce numbers of dust mites in beds.

See how they run

One end of the running track is warmed with hot water, while the other is cooled, producing a temperature and humidity gradient along the course. The researchers saw that the mites raced from the hot, dry end towards cooler, humid conditions, says Wilkinson.

"Mites can't drink water like we can", he explains. "They have to absorb it from the atmosphere using little glands on the surface of their body." Mites cannot survive in conditions below 50% humidity, because they cannot get enough water from the atmosphere.

But the extra water in the air from a quick shower can raise the humidity in a house enough to sustain the mites. "It gives them their daily drink," says Wilkinson. People with mites should open windows or use an extractor fan after having a shower, advises Ucci.

Top tips

The researchers also point out that leaving the duvet on the bed during the day can make a big difference, because it keeps moisture in the sheets and mattress. It's best to leave the covers off, says Ucci. "It gives you an excuse for a messy bedroom," adds Wilkinson.

Even better, staying in bed longer raises the temperature of the mattress enough to make the mites uncomfortable, despite the extra moisture produced by a sleeping body. And simply raising the bedroom temperature from 16°C to 18°C can cut mite numbers by a factor of ten.

Climate change could also have an impact. The team calculates that a typical London bed could have 80 times more mites by 2050 if the world's warming increases humidity levels as predicted.

The researchers are now putting 'mite pockets' in people's beds, along with sensors to record the temperature and humidity, in 36 houses around the UK. "People assume that a bed is a homogeneous environment, but it's actually very variable," says Wilkinson. They have already found that a single mattress can sustain up to 1.5 million mites in the right conditions.

The work was presented at a showcase of research funded by the UK's Engineering and Physical Sciences Research Council, held in London on 17 November.


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