WHY IT PAYS TO TAKE OFF YOUR SHOES

Researchers have discovered 60 per cent of dust comes from outside.

Although some particles get blown in by wind or arrive by other means, the most common method through the front door is on the soles of shoes.

But it is more than just an added chore for whoever does the cleaning, said the researchers in the journal Environmental Science and Technology.

While indoor dust includes unsavoury items such as human skin and hair, outdoor ingredients can include poison and pollutants. The most serious found in the study of 100 homes were arsenic and lead, said the research team from the University of Arizona.

Although usually found in harmless microscopic amounts, arsenic and lead in dust could be a danger to children who put toys in their mouths, said the study.