Carbon monoxide poisoning

Carbon monoxide is a poisonous gas that has no smell or taste. Breathing it in can make you unwell. It can kill if you're exposed to high levels. Go immediately to your local emergency department if you think you've been exposed to carbon monoxide and have symptoms (see below).

Symptoms of carbon monoxide poisoning

The symptoms of carbon monoxide poisoning aren't always obvious, particularly during low-level exposure.

A tension-type headache is the most common symptom of mild carbon monoxide poisoning. Other symptoms include:

The symptoms of exposure to low levels of carbon monoxide can be similar to those of food poisoning and flu. But unlike flu, carbon monoxide poisoning doesn't cause a high temperature (fever).

The symptoms can gradually get worse with long periods of exposure to carbon monoxide, leading to a delay in diagnosis.

Breathing in high levels of carbon monoxide gas can cause more severe symptoms. These may include:

  • impaired mental state and personality changes (intoxication)
  • vertigo – the feeling that you or the environment around you is spinning
  • ataxia – loss of physical co-ordination caused by underlying damage to the brain and nervous system
  • breathlessness and tachycardia (a heart rate of more than 100 beats per minute)
  • chest pain caused by angina or a heart attack
  • seizures – an uncontrollable burst of electrical activity in the brain that causes muscle spasms
  • loss of consciousness – in cases where there are very high levels of carbon monoxide, death may occur within minutes

Causes  of carbon monoxide leaks

Carbon monoxide is produced when fuels such as gas, oil, coal and wood don't burn fully.

Burning charcoal, running cars and the smoke from cigarettes also produce carbon monoxide gas.

Incorrectly installed, poorly maintained or poorly ventilated household appliances – such as cookers, heaters and central heating boilers – are the most common causes 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.

Treating carbon monoxide poisoning

Seek medical advice from your GP if you think you've been exposed to low levels of carbon monoxide.

Go immediately to your local emergency department if you think you or someone with you has been exposed to carbon monoxide and the symptoms suggest high levels (see above).

Your house will also need to be checked for safety before anyone returns.

Complications of carbon monoxide poisoning

Long periods of significant exposure to carbon monoxide can cause serious complications, including brain damage and heart problems. In very severe cases, it can result in death. 

Preventing carbon monoxide poisoning

It's important to be aware of the dangers and identify any appliances in your house that could potentially leak carbon monoxide. 

What to do in an emergency

If you think you might be suffering from carbon monoxide poisoning, you should:

  • immediately turn off all appliances if it is safe to do so
  • ventilate your home by opening windows and doors
  • stay outside in the fresh air
  • seek medical help from a qualified healthcare professional

Carbon monoxide poisoning can also cause long-term health problems if you’re exposed to low doses over a long period of time.

Appliances should not be used again until they have been serviced by a registered engineer.

Being aware of the signs

It's very important to be aware of the risk of carbon monoxide poisoning and to look out for warning signs.

You should suspect carbon monoxide poisoning if:

  • other people in your house, flat or workplace fall ill with similar symptoms
  • your symptoms disappear when you go away – for example, on holiday – and return when you come back
  • your symptoms tend to be seasonal – for example, if you get headaches more often during the winter when the central heating is used more often
  • your pets also become ill


The information on this page has been adapted from original content from the NHS website.

For further information see terms and conditions.

This page was published November 2017

This page is due for review September 2019

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