Chemical pollutants can be released from many sources in the home, where typical pollutant levels are about 20 times higher than outside.
Derrick Crump, who leads work on indoor air pollutants at the Building Research Establishment, near Watford, recently completed a survey of the situation in 500 English homes.
It revealed that the average amount of formaldehyde, an organic chemical used in furniture glue and disinfectants, was 25 parts per billion. Crump believes that some homes may have levels above the maximum safe amount recommended by the World Health Organisation.
Another study, shows that levels of benzene, a carcinogen, were higher in homes with an attached garage.
In a third study, Crump examined chemicals given off by pillows, which people are in contact with for eight hours a day.