Carbon Monoxide poisoning

Carbon Monoxide (CO) is a poisonous gas that you cannot smell, taste or see. It is formed through combustion and is produced in car exhaust fumes, fires and from tobacco smoke. In addition, fuels such as gas, oil, coal and wood that do not burn fully.

Gas, oil, coal and wood are sources of fuel used in many household appliances, including:

  • boilers
  • gas fires
  • central heating systems
  • water heaters
  • cookers
  • open fires

Incorrectly installed, poorly maintained or poorly ventilated household appliances such as cookers, heaters, and central heating boilers are the most common cause of accidental exposure to Carbon Monoxide.

The risk of exposure to Carbon Monoxide from portable devices may also be higher in caravans, boats and mobile homes.

Other possible causes of Carbon Monoxide poisoning include:

  • blocked flues and chimneys - this can stop Carbon Monoxide escaping, allowing it to reach dangerous levels
  • burning fuel in an enclosed or unventilated space - for example, running a car engine, petrol-powered generator or barbecue inside a garage, or a faulty boiler in an enclosed kitchen
  • faulty or blocked car exhausts - a leak or blockage in the exhaust pipe, such as after heavy snowfall, could lead to a build-up of Carbon Monoxide
  • paint fumes - some cleaning fluids and paint removers contain methylene chloride (dichloromethane); this substance is broken down by the body into Carbon Monoxide
  • smoking shisha pipes indoors - shisha pipes burn charcoal and tobacco, which can lead to a build-up of Carbon Monoxide in enclosed or unventilated rooms

Symptoms of Carbon Monoxide poisoning

After Carbon Monoxide is breathed in it enters your bloodstream and mixes with haemoglobin (the part of red blood cells that carry oxygen around your body) to form Carboxyhaemoglobin. When this happens the blood is no longer able to carry oxygen and this lack of oxygen causes the body's cells and tissues to fail and die.

The symptoms of Carbon Monoxide poisoning are not always obvious, particularly during low-level exposure. A tension-type headache is the most common symptom of mild Carbon Monoxide poisoning.

Other symptoms include:

  • dizziness
  • feeling and being sick
  • tiredness and confusion
  • stomach pain
  • shortness of breath and difficulty breathing

If you are a smoker

Non-smokers have very low levels of CO in their blood but smoker's levels are usually much higher. The heavier the smoker, the higher the CO levels and the greater the dependence on nicotine.

Having high levels of Carbon Monoxide in your bloodstream is very dangerous to health, and smoking is in effect a 'slow-motion suicide'.

Get help to stop smoking

How CO gets into your body

When you inhale smoke from a cigarette CO is absorbed into your blood through the lungs.

Oxygen is carried around the body by red blood cells.

CO binds with haemoglobin in the red blood cells to form Carboxyhaemoglobin (COHb), preventing red blood cells from carrying oxygen. CO binds with haemoglobin 200 times more readily than oxygen.

COHb concentrations of 3% are rarely found in non-smokers exposed to town air, whereas concentrations of 5-15% are often found in smokers, thus depriving the body of oxygen.

What CO does to your body


To compensate for the shortage of oxygen, the heart has to work harder (beat faster) to get enough oxygen to all parts of the body. The heart itself gets less oxygen increasing the risk of heart damage.


The COHb causes thicker blood and the arteries get coated with a thick fatty substance. This causes circulation problems and high blood pressure, with increased risk of a heart attack and stroke. Hands and feet can become colder as less blood circulates to the extremities.


The reduced supply of oxygen means you can easily get out of breath when exercising as there is little extra oxygen available for the increased demand. The lack of oxygen can also cause tiredness and lack of concentration.


The supply of oxygen required by the baby for healthy growth is reduced when the pregnant mother smokes.

Your baby receives all the oxygen, nutrients and antibodies they need from your blood supply. When you smoke (or if you breathe in other people's smoke) the Carbon Monoxide, and other damaging chemicals, restricts the oxygen your baby gets.

This affects your baby's growth and development and causes your baby's heart to beat harder every time you smoke.

Smoking also increases the risk of:

  • miscarriage
  • stillbirth
  • low birthweight
  • premature birth
  • sudden infant death syndrome (SIDS)

Get help to stop smoking

If you or someone would like help to stop smoking please contact us on 0300 126 3000.

Last updated 06 October 2022