An interactive map shows the hotspots of a radioactive gas in south London which is colourless, odourless and tasteless.
Radon is formed by radioactive decay from the small amounts of uranium that can be found naturally in all rocks and soils.
This means that it is everywhere.
Public Health England, however, states that "every building contains radon but the levels are usually low.
"The chances of a higher level depend on the type of ground."
The radiation emitted from the elements can increase the risk of cancer and it appears that those living in rural areas are surrounded by more levels of this radioactive gas than more urban areas like London.
Public Health England has released a map showing where high levels are more likely.
The darker the colour, the greater the chance of a higher level.
The chance is less than one home in a hundred in the white areas and greater than one in three in the darkest areas.
A broad look at south London shows low levels of radon, with hotspots in some particular areas.
Here are how some locations in south London fare according to the map:
Bexley
There is a predominately low risk of radon around the area.
Some parts of this 1km grid square are in bands of elevated radon potential. Maximum radon potential is 1-3%.
Lewisham
Some parts of this 1km grid square are in bands of elevated radon potential. Maximum radon potential is 1-3%.
Bromley
All parts of this 1km grid square are in the lowest band of radon potential. Less than 1% of homes above the Action Level.
Greenwich
All parts of this 1km grid square are in the lowest band of radon potential. Less than 1% of homes above the Action Level.
Dartford
Some parts of this 1km grid square are in bands of elevated radon potential. Maximum radon potential is 1-3%.
Southwark
All parts of this 1km grid square are in the lowest band of radon potential. Less than 1% of homes above the Action Level.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here