Slowly. Insidiously.
That's how radon gas gradually first contaminates your home, and then your body.
For an estimated 350 people every year, the consequence is lung cancer.
Part of the problem is that this radioactive gas is colourless, odourless and tasteless.
However, it's also easily detectible.
This begs the million-dollar question: why is this silent killer still a problem in 2022?
170,000 homes are located in high-radon areas - an increase of 45,000 on a survey from 2002.
If nothing is done, then it appears likely the death toll will not just grind-on but increase.
I first heard about radon from the Fine Gael TD for North Kerry, Jimmy Deenihan, when appointed RTÉ's Environment Correspondent in 2002.
He told the Dáil in 2005 how a house in his constituency had radon concentrations almost 250 times higher than what was deemed acceptable.
Indeed, the deputy said it was one of the highest radon levels ever detected in Europe.
Two people in the house died from lung cancer, even though they were non-smokers and healthy.
He added: "Along a one-mile stretch of road, which includes this household, nine people - many middle-aged and younger - have died from cancer over the past decade."
It struck me that this naturally occurring gas, which is generated from the breakdown of rocks and soils, was causing untold but avoidable carnage.
The deaths continue, despite considerable efforts to raise public awareness.
The Radiological Protection Institute of Ireland, and now the EPA, have alerted people to dangers of the radioactive gas, identified hot-spots, and promoted the use of radon detectors.
Part of the problem, it appears, is a reluctance or reticence by people living in high-radon areas to get their homes checked.
That was proven when the RPII contacted 2,500 households in Castleisland - a hotspot in north Kerry - about high-radon levels and urged them to get radon test kits.
Only 16% of households took-up the offer.
The finding led me to believe that the government needed to legislate on the issue as otherwise the problem would continue.
Some regulations have been forthcoming.
Employers in hotspots are now legally obliged to take remedial measures, and then retest, if radon readings are above what's deemed to be acceptable.
Radon barriers are now obligatory when new houses are being built.
That still leaves two big problems: 1: existing homes are not being routinely checked; 2: radon barriers are not 100% effective and regular re-testing is required.
The solution, I've long felt, is for there to be an obligation for a house to be tested for radon before it can be sold or rented.
After all, if we compel people to have Building Energy Rating certificates - why not ensure the same house isn't a cancer laboratory too?
Opposition parties called this week for speedy action, on foot of the EPA report.
The Social Democrats housing spokesperson Cian O'Callaghan pointed out that the 2019 National Radon Control Strategy, Phase 2, recommended that radon testing, and where necessary remediation, should be compulsory when a home is being sold in high radon areas.
He said: "Currently 95% of Irish householders are living in homes that have not been tested for radon. Meanwhile, there is no requirement for those selling or renting their homes to test for radon levels. This must change."
Labour deputy Duncan Smith raised the issue in the Dáil.
He asked Tánaiste Leo Varadkar: "While building regulations for new homes require the installation of radon membranes, are there any plans to make it obligatory to test for radon when a house is either sold or rented? Will the State carry out radon tests on homes?"
Mr Varadkar replied: "This is an important issue, and the deputy asks some valid questions, I'm afraid I don't have an up-to-date answer with me."
However, it appears that legislation is the way the Government is going to go.
It's currently waiting for a report from the National Radon Control Strategy group, which will list actions to be taken up to 2024.
A Government spokesperson said: "These actions include working with relevant agencies to ensure that conveyancing legislation includes a requirement that radon testing, and where necessary remediation, is compulsory when selling a home in a high radon area."
They are also examining the question of "financial supports" for households who've detected a problem and need to remediate.
While that sounds like good news - albeit rental properties are not mentioned - legislation can't come quick enough.
If the statistics are to be believed, more 7,000 people have died from radon related lung cancer over the past 20 years.
