Air is a mixture of gases including:

• Nitrogen (78%) which is an inert chemical – it seldom reacts with other chemicals at normal temperatures so it doesn’t damage our delicate lungs tissues.
• Oxygen (21%). In our cells oxygen combines with the carbon and hydrogen atoms from food producing energy, carbon dioxide (CO2) and water (H2O). This chemical reaction is called oxidation. The energy is used for other chemical reactions in our cells and the water and carbon dioxide is breathed out.
• Water vapour
• Other gases including carbon dioxide, methane and other greenhouse gases.

If the air inside or outside smells bad it may be dangerous for our body. Our sense of smell can detect many toxic substances. Smoke from bush fires and indoor stoves and heaters contains fine particles that can damage the lungs and blood vessels, some glues and paints give off gases that can cause damage to the brain and the smells from rotten food warns us of high numbers of potentially dangerous microbes.

Some highly toxic gases such as carbon monoxide have no odour. Gas cooktops and heaters produce air pollutants such as nitrogen dioxide and carbon monoxide that can increase the risk of childhood asthma and respiratory disease in all ages. Indoor gas cooking has been estimated to be responsible for up to 12% of asthma in childhood and is a similar level of risk to passive smoking.