Radon gas tests to be offered to Gloucestershire households
People living in "hotspots" for radon are to be offered free tests for the naturally-occurring radioactive gas.
About 18,000 households in areas of Gloucestershire where the risk of radon is highest are to be written to by Public Health England (PHE).
Scientists say some homes in areas covered by Cotswold District, Forest of Dean District and Cheltenham Borough councils are most at risk.
It is believed the gas can lead to lung cancer deaths, especially in smokers.
Neil McColl, from the PHE's Centre for Radiation, Chemicals and Environmental Hazards, said: "It has long been known that the Cotswolds and parts of Gloucestershire are radon hotspots.
'Long term exposure'
"Parts of Cornwall, Aberdeenshire and West Oxfordshire also have high levels and over the years we have worked with people there to help them find out if their home is affected and if it is, to take action to reduce their radon levels.
"It's important people do act because long term exposure to high levels of radon can lead to lung cancer."
Mr McColl said PHE would be writing to households over the next week to offer a free test.
The test involves placing two plastic detectors, described as being "about the size of a biscuit", in key positions around the home.
After three months the detectors are posted to PHE to be analysed and the radon level calculated.
'Every home different'
If levels are high householders will get advice on how to reduce levels.
Dr Peter Brambleby, director of public health for Gloucestershire, said: "Testing for radon is easy and important.
"Although you may live in a radon affected area it's important to remember that every home is different.
"Just because your neighbour isn't exposed to high levels, it doesn't mean you won't be, that's why testing is so important."
Letters will be sent to about 8,100 households across Cotswold District Council's area, 9,700 in the Forest of Dean District Council's area and about 190 to addresses in Cheltenham Borough Council's area.