Harm from second-hand smoke occurs when you are exposed to tobacco being smoked near you. Second-hand smoke comes from the burning end of the cigarette and the smoke exhaled by smoker. You breathe in more than 4,000 chemicals when you are around someone who is smoking, of which 69 chemicals are carcinogenic. Concentrations of the chemicals vary with the distance from the smoker.

Exposure to passive smoking can take place in a variety of settings, both public and private. Most common are homes and cars. Exposure to tobacco smoke increases the risk of: lung cancer, respiratory and cardiovascular disease, exacerbation of asthma and reduces lung function.

Children are at particular risk from the effects of passive smoking because they have an increased risk of developing chest infections during their first five years. Babies who are exposed to cigarette smoke are also at a greater risk of sudden infant death syndrome (SIDS), which is also known as cot death. As well as making children more vulnerable to ear infections, such as otitis media, passive smoking makes children more likely to develop asthma.