Amid winter’s freezing grip, it’s the season for cosy home comforts (or Hygge, as it’s known in Denmark), in the shape of crackling wood fires, flickering scented candles to perfume our snugly draught-proofed homes – and the tempting aroma of a hot meal bubbling on the cooker.
Alarmingly however, scientists are warning that all of these may raise our risk of developing serious illnesses including cardiovascular disease, dementia, depression and lung cancer.
This is because they release millions of minute particles and toxic chemical gases that damage our tissues.
Most worrying at this time of year is the temptation to snuggle up to a trendy wood-burning stove.
Latest figures from the UK wood-burner industry, the Stove Industry Association (SIA), show Britons have been buying them at record levels – snapping up more than 2,000 of them in 2022, a 40 per cent rise from the previous year.
Meanwhile, a report by the Institute of Fiscal Studies warned three-quarters of UK domestic combustion emissions (which also include gas boilers and cookers) in 2022, came from wood-burning.
Indeed as well as sending smoke up the chimney, wood-burning stoves fill our indoor air with very harmful substances, especially sooty particulate matter, known as PM2.5 – which measure 2.5 micrometres or less in diameter; about 3 per cent the width of a human hair.
Once inhaled PM2.5 travel in our bloodstream and can penetrate deep into our organs, where they can cause inflammatory damage that is linked to serious illnesses such as heart disease, depression and lung cancer.
Britons have snapped up wood-burning stoves at record levels in recent years but some reports suggest they fill our homes with harmful substances
Scientific evidence against wood-burning stoves in particular has been building in the past 20 years, to the point where in September, the Royal College of Paediatrics and Child Health called on the Government to phase out domestic wood-burning in urban areas until it is ultimately banned, to prevent damage to developing brains and bodies.
Indeed it is not only our brains that are at risk.
A 2017 analysis of 17 medical studies, found that an increase in exposure to PM2.5 of ten microgrammes per cubic metre of air (μg/m3) raises our risk of lung cancer by 8 per cent and dying from the disease by 11 per cent, reported the journal Oncotarget.
A 2020 University of Sheffield study found on average PM2.5 exposure from wood-burners ranged from 27.34 to 195.83 microgrammes per μg/m3 (the Government’s safe target is ten).
Another 2020 study, reported in the journal Atmosphere, found that the concentration of PM2.5 in the home rises by almost 200 per cent when a wood stove is burning. The figure can leap up to 400 per cent higher after the stove door is opened to add more fuel.
Such findings show how Britain’s deadliest cancer toll could continue to rise due to indoor pollution. Currently one in 14 men and one in 13 women are expected to be diagnosed with lung cancer, according to Cancer Research UK.
And even occasional use of wood-burning stoves can be perilous.
Last year, a study found that people who used their wood-burner for a month or more each year saw their lung cancer risk jump by 68 per cent.
Dr Suril Mehta, an epidemiologist at the US National Institute of Environmental Health Sciences, who co-authored the study, said: ‘Even occasional indoor wood-burning can contribute to lung cancer in populations where indoor wood burning is not the home’s predominant fuel source.’
This pollution may also threaten our cardiovascular health.
A New York University-led review of scientific evidence last year in the International Journal of Cardiology: Cardiovascular Risk and Prevention warned that exposure to PM2.5 significantly raises the risk of heart attack, stroke and heart failure.
This is caused primarily by PM2.5 sparking chronic inflammation throughout the cardiovascular system.
Indeed the particulates from wood-burning smoke cause much higher levels of damaging inflammation to cardiovascular cells than even particulates from diesel engine exhausts, according to a 2012 lab study by Copenhagen University.
Mounting concerns over harmful pollutants from stoves mean that since January 2022, only wood-burners with less polluting designs (bearing the Ecodesign mark) are legally allowed to be sold in UK.
These are estimated to emit up to 80 per cent less than older stoves, according to the SIA.
But medical authorities remain unconvinced.
In 2022 Professor Chris Whitty, the chief medical officer for England at the time, published a report on air pollution which warned that even Ecodesign wood-burners produce 450 times more toxic air pollution than gas central heating (that’s about the same rate as 25 ten-year-old diesel lorries).
The worst of all home-polluters are open fires.
Professor Chris Whitty, former chief medical officer for England, warned in 2022 that more eco-friendly stoves still produce 450 times more toxic air pollution than gas central heating
Air-quality researchers at King’s College London report that more than two-thirds of households that burn wood still use open fires.
These emit ten times more particle emissions than closed Ecodesign stoves, and are banned in some UK areas under the Clean Air Act.
‘People should simply avoid using wood-burning stoves and open fires,’ says Amy McCarron, a scientific outreach officer at the University of Stirling, who last year published a study on people’s behaviour around indoor pollution.
‘Many use them not as a primary source of heat – they have central heating – but to create a cosy ambiance, which is unnecessary and perilous.’
Our homes are beset by multiple other sources of harmful (although invisible) indoor air pollution, too.
One of the most significant is scented candles and air fresheners.
A report in the journal Indoor Environments found that the UK home-fragrance market generated more than £540million in 2023 and is expected to surpass £950million by 2030.
Ironically, this growth is ‘spurred by householders wanting to improve their indoor air quality’, says Dr Ann Marie Coggins, a senior lecturer in exposure science at the University of Galway, who co-authored the report.
Burning scented candles also comes with a risk as experts say they can produce chemicals which include gases such as carbon monoxide and sulphur dioxide
Burning scented candles can send indoor particulate concentrations over 15 times the World Health Organisation’s safe limits.
‘They produce a complex mix of chemicals and particulate matter, including toxic gases such as carbon monoxide, sulphur dioxide and oxides of nitrogen, which can have a negative effect on lungs and airways,’ says Dr Coggins.
Particulates from candles can also worsen some existing conditions such as asthma, according to the report, and long-term exposure can increase the risk of heart disease, lung cancer and chronic bronchitis.
Moreover burning scented candles is a major source of formaldehyde, which is described by the US Government’s National Toxicology Program as a ‘human carcinogen’. It is most closely linked with cancers of the nose and throat.
Meanwhile, air fresheners could lead to negative health impacts such as migraines, asthma attacks and dermatitis. A 2015 study that involved Public Health England’s Centre for Radiation, Chemical and Environmental Hazards, warned that plug-in air fresheners also produce ‘considerable’ levels of formaldehyde.
Specific ingredients found in plug-in air-fresheners include petroleum products and p-dichlorobenzene, which have been linked with a raised risk of asthma in adults and children. Naphthalene is also sometimes used, which has been shown to cause tissue damage and cancer in the lungs of rats and mice in laboratory studies.
Dr Coggins suggests that we minimise dangers by ‘only using candles and air fresheners in well-ventilated spaces, and ‘always snuff out candles outdoors’ as the highest level of particulates is released when they are put out.
And if you’re cooking this festive season, that could also be another major source of indoor pollution.
The UK National Centre for Atmospheric Science warns that gas hobs are a main source of toxic indoor emissions, including nitrogen oxides and carbon monoxide. Electric hobs don’t emit such sooty particulates.
In August, a University of Birmingham study warned that with gas cooking, indoor pollution levels consistently exceed World Health Organisation safety limits, particularly in the kitchen.
The researchers said particulate matter from gas cookers can spread throughout the house and concentrate upstairs in bedrooms, as warm air rises up through the building.
What you cook, and how you cook it can make a significant difference, according to a separate study by York University last year.
This found that frying spices in hot oils produced particularly high concentrations of potentially lung-damaging chemicals called reactive monoterpenes.
Switching to trendy air fryers could make a huge difference, according to Christian Pfrang, a professor of atmospheric science at the University of Birmingham.
He told the Mail: ‘We recently conducted series of experiments, cooking chicken in various ways, and found that stir-frying and pan-frying produced 100 times more indoor pollution than air-frying.’
Professor Pfrang, who stressed his work is not sponsored by air-fryer manufacturers, adds: ‘It is reasonable to assume that the difference is in the amount of cooking oil involved, which is minimal with air fryers. Cooking temperatures are also lower.’
For anyone using conventional cookers, he urges: ‘Switch on the extractor hood. Just ten minutes of gas-hob use without the extractor can fill the house with pollution. Running the extractor for 20 to 30 minutes will prevent this pollution spike.’
One further problem propelling our indoor air pollution crisis is our understandable urge to make our homes as airtight as possible – to keep in all that expensive cosy heat. Yet failing to ventilate our homes can present a serious health peril.
‘When people think about air pollution, they most often think of outdoor air, with its traffic congestion and industrial chimneys,’ says Ms McCarron.
‘They often think that closing windows protects them from air pollution. We know that’s not the case. Increase your home ventilation by opening windows and doors.’
Another option,if opening windows proves too cold and unbearable, is to populate the house with pot plants.
Professor Pfrang led research on different types of pot plants in laboratory chambers, and found ‘they have a measurable effect in reducing indoor pollution in the form of emissions from gas hobs and wood-burning stoves’, it was reported in the journal Air Quality, Atmosphere & Health in 2022.
This was particularly true with reducing nitrogen dioxide emissions, which can inflame the lining of the lung and reduces immunity to infections such as bronchitis.
‘We found that plants can take nitrogen dioxide out of the air,’ says Professor Pfrang.
‘The peace lily (Spathiphyllum wallisii) was slightly better than the corn plant (Dracaena fragrans) and fern arum (Zamioculcas zamiifolia), but generally they seem pretty similar.’
Amid all the grim news about our cosy kit, at least a host of potted greenery could bring a new dose of cheer to our winter homes.
