The fact that smoking is harmful to human health can not be over-emphasised. Smoking is not just harmful to the smoker but to people who stay around and inhale the dangerous mix of chemicals.
Tobacco smoke is a mixture of approximately 7000 chemical compounds, many of these are toxic to the cells of the human body. About 70 of these substances like formaldehyde and benzene are known to be capable of causing cancer.
Since there is no safe amount of tobacco smoke, the best for the good health is to always avoid inhalation. The long-term consequences for passive smokers are similar to the consequences for smokers due to the accumulation of toxic substances in the body.