If you were asked what the largest source of pollution is that people breathe, your answer might include power plants, diesel lorries, or cars. But all these answers would be wrong.

Since most people spend between 65 and 90 percent of their time indoors, it is indoor sources of air pollution, not outdoor air pollution, which have a greater impact on human health.

Simply walking around your home can increase your exposure to particulate pollution, research reveals.

In a new study, the amount of particulates stirred up by household activities such as walking, making the beds and vacuum cleaning was measured with surprising results.

Many studies have researched the health-threatening effects of cooking and smoking in the home but this new research looked at the re-suspension of house dust due to human activities such as housework.

"The more vigorous the activity, the more dust you get," says Andrea Ferro of Stanford University in California.

And cleaning up dust only partially helps. Vacuum cleaning itself creates a flurry of dust, not all of which ends up in the machine.

Next to second-hand cigarette smoke and cooking emissions, house dust re-suspended by indoor human activity is the largest source of particulate matter (PM) that we breathe.

House dust contains many pollutants, including pesticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), molds, allergens, and lead and other heavy metals.

These pollutants are either tracked in with shoes, infiltrated through doors, windows and cracks, or are generated indoors. They then collect on surfaces and are re-suspended with human activity. Just sitting on furniture increases concentrations of these pollutants as much as vacuuming.

How to keep pollutants to a minimum

Carpets emit ten times more dust than wood so wood or vinyl floors are useful in keeping down dust.

“Removing carpeting and extra cloth furnishings from the home,” says Andrea, “and dusting with a damp rather than dry cloth, keeping the home as dust-free as possible, are some of the important measures one can take to reduce their exposure to particulate matter from indoor human activity.”

Ventilating the house well, especially after major activity such as cleaning, will keep particulates down.