**3.9 Environmental tobacco smoke (ETS)**

Environmental tobacco smoke is generated by the combustion of tobacco smoke. It is commonly emitted with combustion, which is actively exhale from the smoker. Tobacco smoke is composed of more than 4000 toxic compounds, most of them well known to have carcinogen effects [36]. There are two types of environmental tobacco smoke, which can be divided into side stream smoke which is the smoke from tobacco that is released from the end of a burning cigarette or tobacco pipe. Mainstream smoke refers to the smoke that is inhaled by a smoker that is actively exhaled to the environment and subsequently inhaled by a second person causing inhalation exposure. Side stream smoke is also of danger if prolonged exposure of time, side stream can persist affecting the smoker and not smoker in close rooms [37]. Several factors had been recognized that can affect the amount of side stream smoke which is humidity, temperature, open ventilation versus close ventilation and number of active smokers in the room. At this moment there is some data suggesting that second hand smoking can cause obstructive lung diseases as well however it's something that under investigation.
