Carbon monoxide (CO) is an odourless, colourless gas which forms when the carbon in fuels doesn’t completely burn. It is usually generated by motor vehicles and industry but can also be formed during bushfires. Indoors, carbon monoxide is formed by unflued gas heaters, wood-burning heaters, and contained in cigarette smoke.

Carbon monoxide levels are typically highest during cold weather, because cold temperatures make combustion less complete and traps pollutants close to the ground.

Carbon monoxide can cause harmful health effects by reducing the amount of oxygen reaching the body’s organs (like the heart and brain) and tissues. At extremely high levels, carbon monoxide can cause death (carbon monoxide poisoning).

Potential health effects from exposure to carbon monoxide:

• Flu-like symptoms such as headaches, dizziness, disorientation, nausea and fatigue
• Chest pain in people with coronary heart disease
• At higher concentration: impaired vision and coordination, dizziness and confusion
• Potentially serious health effects on unborn babies when exposed to high levels

To learn more, visit our section ‘Who is affected by air pollution’ and ‘Simple steps to protect your health’. For further information on bushfire smoke, unflued gas heaters or wood-burning heaters, please see our section on air quality factsheets.