Carbon monoxide (CO) is an odourless, colourless, tasteless gas produced by incomplete combustion of carbon-containing fuels. In the domestic environment it is generated by gas boilers, gas cookers, gas fires, paraffin heaters, wood-burning stoves, and petrol-powered tools used indoors. It kills around 40 people per year in England and Wales from acute poisoning, and chronic low-level exposure causes neurological symptoms that are frequently misdiagnosed as migraine, flu, or depression. It is arguably the most immediately dangerous chemical in the domestic environment.
Where it's found
Gas boilers — particularly older boilers and those that are poorly maintained, blocked, or inadequately ventilated — are the primary source of CO incidents in UK homes. Gas cookers generate CO during normal use, particularly when burners are misaligned or ring supports block airflow. Blocked flues and chimneys on any gas or solid fuel appliance cause CO to spill into the room rather than vent outside. Paraffin heaters used in garages or as supplementary heating. Wood-burning stoves and open fires with inadequate draw. Petrol-powered generators, lawnmowers, and pressure washers used in garages or near open windows. Barbecues brought indoors to heat rooms — a major cause of fatal CO poisoning.
Routes of exposure
Inhalation is the sole exposure route. CO binds haemoglobin with 200–300 times the affinity of oxygen, forming carboxyhaemoglobin (COHb) that cannot carry oxygen. Even low concentrations of inhaled CO rapidly increase blood COHb to levels that cause symptoms. Chronic low-level exposure from a slow boiler or cooker leak accumulates insidiously over hours to days, causing progressively worsening symptoms that may not be recognised as CO-related. Acute high-level exposure from a sudden blockage or appliance failure causes rapid incapacitation and death.
Health concerns
Acute CO poisoning causes headache, nausea, dizziness, confusion, and ultimately loss of consciousness and death from cerebral hypoxia. It kills approximately 50 people in the UK per year from accidental domestic poisoning and sends thousands more to emergency departments. Chronic low-level CO exposure causes persistent headache, fatigue, cognitive impairment, depression, and mood changes that are frequently attributed to other causes and result in delayed or missed diagnosis. Post-poisoning neurological sequelae — including memory impairment, personality change, and movement disorders — can persist for months to years after acute incidents. Foetal damage from CO poisoning during pregnancy results in foetal hypoxia and can cause foetal death, brain injury, and developmental disorders.
Evidence
The acute toxicity of CO via haemoglobin binding and tissue hypoxia is established pharmacology and biochemistry — this is among the best-characterised mechanisms of any toxic gas. The scale of domestic CO poisoning mortality and morbidity is documented through national death and hospital admission registries. The neurological sequelae of non-fatal poisoning are well characterised in clinical series. The health burden from chronic low-level exposure (the so-called "slow poisoning" scenario) is harder to quantify but is supported by clinical case series and is increasingly recognised.
Who's most at risk
Everyone is at risk from CO poisoning, but certain groups face greater harm: pregnant women and foetuses (CO crosses the placenta and causes disproportionate foetal harm at maternal COHb levels that cause only mild symptoms in the mother). People with cardiovascular disease or anaemia are less able to compensate for reduced oxygen delivery. Sleeping individuals are at risk of fatal poisoning before waking symptoms occur. Older people may attribute early symptoms to existing health conditions and not recognise CO exposure.
Regulatory status
RegulationAll domestic gas appliances must be annually serviced by a Gas Safe registered engineer in UK rental properties under the Gas Safety (Installation and Use) Regulations 1998. CO alarms are compulsory in new build properties in England and in all rental properties where there is a solid fuel appliance. CO alarms in properties with gas appliances are currently advisory rather than legally mandatory in England, though Scotland and Wales have stronger requirements. Gas Safe Register provides the official register of qualified gas engineers.
How to reduce your exposure
Install at least one CO alarm on each floor of your home — choose an alarm that is CE marked to EN 50291 standard and replace it every 7–10 years. Have your boiler serviced annually by a Gas Safe registered engineer. Never use a barbecue, petrol generator, or camping stove indoors or in an enclosed space. Know the symptoms of CO poisoning: headache, dizziness, nausea, and confusion — particularly if symptoms improve when you leave the house. If you suspect CO, get everyone out, call 999, and do not re-enter.
The nutrition connection
Carbon monoxide is primarily a safety emergency rather than a nutritional topic, but there is a metabolic connection worth noting: CO poisoning causes tissue hypoxia that stresses the same cellular machinery — mitochondrial oxidative phosphorylation — that nutritional status profoundly influences. Adequate iron status (essential for haemoglobin function), B vitamins (required for cellular respiration), and antioxidant status (countering oxidative stress from hypoxic injury) all influence recovery capacity from low-level CO exposure. More directly, CO poisoning is a kitchen safety issue — the gas cooker is a CO source in every home, and ventilation during cooking is the simplest protective measure available.