Secondhand tobacco smoke harms both smokers and non-smokers
It is either smoke that has been inhaled and exhaled by the smoker - called mainstream smoke, or smoke from the burning cigarette tip - called sidestream smoke, which is believed to be four times more dangerous than mainstream smoke.
About half of all children are exposed to smoke at home, it makes them more likely to suffer problems such as bronchitis, pneumonia, increased risk of sudden infant death syndrome, asthma, respiratory symptoms and ear infections.
In adults, it is thought to increase the risk of lung cancer and heart disease.