"The more vigorous the activity, the more dust you get," says Andrea Ferro of Stanford University in California, who led the work. This may be true anywhere. Surprisingly, that includes vacuum cleaning, which creates a flurry of dust, not all of which ends up in the machine. Our homes are filled with dust particles, created by smoking, cooking and heating appliances.

The particles - which are just a few micro metres in diameter - are implicated in asthma and diseases of the heart and lungs. Scientists know a lot about how these particles are created, says Ferro, but what happens to them after they settle on floors and furniture is less clear. Her analysis underlines the fact that much of the dust we breathe comes from particles lurking in carpets, rugs and beds.

Ferro's team set up particle detectors in a house in Redwood City, California, and asked its occupants to perform a range of activities. Two people striding across a rug kicked up dust particles at a rate of almost two milligrams a minute - about half the amount of particulate matter belched out by smoking a cigarette.

Other dusty activities included dancing on a rug and, unsurprisingly, dry dusting. But Ferro's team found that vacuum cleaning generates around half as much dust as simply stomping on the carpet - perhaps because the machine's filter fails to trap all of the particles.

"You're pulling small particles out of the carpet, through the vacuum cleaner's filter, into your air and into your lungs," explains Mark Sippola, an environmental engineer at Lawrence Berkeley National Laboratory in California. What's more, the pollution is concentrated in the immediate vicinity of the cleaner, he says.

It differs from cigarette smoke or cooking fumes, which can dis perse throughout the home. How do you keep exposure to; minimum? "It's kind of an uni avoidable thing - these particles will always be re suspended in the air," Sippola says. But he recommends wood or vinyl floors which harbour fewer particles than carpets. "Carpets have ten times the particle-emission rates of wood," agrees Ferro. But per haps the best strategy is to make sure the home is well ventilated and doesn't contain much dust ii the first place. "I would say should get plenty of fresh air in from outside, try to clean on a day when you can open the windows and leave your shoes at the door, Ferro advises.

Adopted from the writing of
MICHAEL HOPKIN