Carbon monoxide poisoning - Symptoms 

Symptoms of carbon monoxide poisoning 

The signs and symptoms of carbon monoxide poisoning are not always obvious, especially during low-level exposure. Some people may also have a pre-existing condition with similar symptoms.

Low levels of carbon monoxide

The symptoms of exposure to low levels of carbon monoxide (CO) can be similar to those of many other conditions, such as food poisoning and flu. However, unlike flu, carbon monoxide poisoning does not cause a high temperature (fever).

The most common symptoms include:

Your symptoms may be less severe when you are away from the source of the carbon monoxide.

The longer you inhale carbon monoxide, the worse your symptoms will be. You may lose balance, vision and memory. Eventually, you may lose consciousness. This can happen within two hours, if there is a lot of carbon monoxide in the air.

Long-term exposure to low levels of carbon monoxide can also lead to neurological symptoms, including:

  • difficulty thinking or concentrating
  • frequent emotional changes  for example, becoming easily irritated, depressed or making impulsive decisions

High levels of carbon monoxide

If you have breathed in high levels of carbon monoxide gas, it is likely that you will experience 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

At-risk groups

Certain people in your household may be affected by carbon monoxide poisoning more quickly than others. Those at particular risk include:

  • babies and young children
  • pregnant women
  • people with heart or breathing problems

Pets may be the first to show signs of carbon monoxide poisoning because they are vulnerable to the effects of the gas. The smaller an animal or a person is, the faster this will affect them.

If your pet suddenly becomes ill or dies unexpectedly, and death is not related to old age or an existing health condition, you should investigate the possibility of a carbon monoxide leak.


Page last reviewed: 21/06/2014

Next review due: 21/06/2016

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