Carbon monoxide poisoning: symptoms, causes and what to do

The NHS lists these symptoms of carbon monoxide poisoning. The UK Health Security Agency (UKHSA) adds that headaches, tiredness, difficulty thinking clearly and feeling sick are common, and that symptoms can be similar to food poisoning and flu, which makes the poisoning easy to miss.

• A headache.

• Dizziness.

• Feeling sick or being sick.

• Feeling weak, tiredness and confusion.

• Chest and muscle pain.

• Shortness of breath.

• Your face turning hot and red (flushing), though redness may be harder to see on brown and black skin.

• Loss of vision.

The NHS says the symptoms may come and go, and may get worse when you spend time in an affected room or building and get better when you leave or go outside. Other people or pets in the same place feeling unwell at the same time is a useful clue, although the pages used here do not state it directly.

UKHSA explains why long-term low-level exposure is hard to spot: exposure to small amounts of carbon monoxide for a long time may lead to flu-like symptoms with tiredness, headaches, nausea, dizziness, personality changes, memory problems and loss of vision, and it can be hard to tell the difference from other common illnesses.

The NHS says to stop using appliances you think might be making carbon monoxide (such as a boiler, cooker or heater) if you can, go outside, and get medical advice as soon as possible. Do not go back into the affected building until you have advice.

UKHSA adds that if your alarm sounds or you believe there is a leak you should stop using all appliances and leave the property immediately, try to stay calm and avoid raising your heart rate, and not go back in until the emergency services advise. It also says to contact the National Gas Emergency Service to report the incident.

The NHS says to call NHS 111 if you think you might have symptoms of carbon monoxide poisoning. It says to call 999 or go to A&E if you think you or someone else has been exposed and are:

• Finding it hard to breathe.

• Suddenly confused.

• Unconscious, or have lost consciousness.

• Feeling weak.

• Having chest or muscle pain.

UKHSA describes carbon monoxide as a colourless, tasteless, odourless, non-irritating gas produced as a by-product of incomplete combustion of fuels, when there is not enough oxygen. When breathed in, it enters the blood through the lungs and attaches to haemoglobin, the body's oxygen carrier, which reduces the amount of oxygen carried round the body.

The NHS says poisoning is caused by breathing in the gas, and that common household appliances for heating and cooking can produce it if they are not installed properly, are faulty or are poorly maintained.

The NHS says you will need to be checked in hospital if you have carbon monoxide poisoning. You will usually have tests to check the level of carbon monoxide in your blood, and you may be given oxygen through a mask. UKHSA says that when people are removed from the source, their health usually improves and symptoms subside, but it is still important to seek medical advice.

UKHSA says people with diseases that affect the delivery of oxygen to the heart or brain, such as coronary heart disease, angina, asthma or anaemia, are particularly at risk. Children, pregnant women and older people are more at risk of harm after exposure, and children may be more sensitive than adults.

In pregnancy, UKHSA says exposure to high levels can reduce the amount of oxygen reaching the baby in the womb, potentially affecting its growth and development. UKHSA says higher exposure may cause movement problems, weakness, confusion, lung and heart problems, loss of consciousness and death.

The NHS and UKHSA advise the following. UKHSA stresses that an alarm will not go off at lower levels of carbon monoxide, so it should not replace regular servicing of appliances.

• Get a carbon monoxide alarm that makes a loud sound, one for each room containing appliances that burn gas, oil, coal or wood. UKHSA says it should meet British or European standards (BS Kitemark or EN 50291).

• Have heating and cooking appliances properly installed and well maintained.

• Have boilers, heaters and cookers serviced regularly by a qualified and registered engineer, such as Gas Safe Register (gas), HETAS (solid fuel) or OFTEC (oil).

• Keep rooms well ventilated, and keep chimneys and flues clean and unblocked; UKHSA says they should be swept at least once a year by a qualified sweep.

• Do not use a barbecue or camping stove indoors or inside a tent.

• Do not leave vehicles or other engines running in enclosed spaces such as a garage.

• Do not use oversized cooking pots that cover more than one gas ring.

Suspected carbon monoxide poisoning is assessed through NHS 111, A&E or 999, where blood tests and oxygen are available. A GP may also be contacted for advice, as UKHSA suggests, if you feel unwell or are worried.

Appliance servicing is a separate matter and is done by a registered engineer, which you may arrange through your landlord or a private firm. After any suspected exposure, ask which appliance was responsible and make sure it is checked and safe before it is used again.