Second Hand Smoke
People that breathe second-hand smoke are at risk of the same diseases as smokers, including cancer and heart disease.
 
The risks

Second-hand (passive) smoking

Second-hand smoke is the smoke that is breathed back out by a smoker.
Wherever people smoke, it is in the air, although you might not notice it because it is almost invisible and odourless.
Second-hand smoke will still be in a room after two and a half hours. Even if you can't see or smell anything, it's probably still there. Smoking in a car is even worse because all of the smoke is concentrated into a small space.

Second-hand smoke contains 4,000 toxic chemicals
People that breathe second-hand smoke are at risk of the same diseases as smokers, including cancer and heart disease
It is estimated that second-hand smoke causes thousands of deaths each year
Children are particularly affected because their bodies are still developing
 
Other people’s health

Obviously, with all the chemicals and toxins in tobacco smoke, it’s going to damage your health if you breathe it in – whether you are a smoker or not.
In fact, when a person smokes a cigarette, they only inhale 15% of the tobacco smoke themselves, so the rest escapes into the air for anyone around to breathe in.

Studies show that if a non-smoker spends over two hours in a smoky room, they will have inhaled the equivalent of four cigarettes.
Second-hand smoke also contains twice as much nicotine and tar and five times the amount of carbon monoxide than the smoke inhaled by the smoker.
Pregnant women should definitely not smoke, but even breathing in other people's smoke can cause real damage to an unborn baby, its health and its weight.
Non-smokers who are married to a smoker suffer up to 60% higher risks of developing cancer or heart disease.
Similarly, children subjected to passive smoking in the home are more likely to suffer breathing difficulties, coughs, ear infections, or pneumonia, and so have to take more time off school. Passive smoking is linked to poor results at school and severe behaviour disorders.
Passive smoking in the short term can irritate the eyes, nose and throat and result in a headache, cough, chest pain, dizziness or sickness.
For people with asthma, the effects of passive smoking are even more severe, as they may suffer serious respiratory problems and wheezing. Asthmatic children are more at risk as their lungs are still developing.