Second-hand smoke contains carcinogens

Second-hand smoke contains more than 4,000 chemicals, many of which are irritants, toxins and poisons including arsenic, benzene and cyanide. More than 50 are known carcinogens that can cause cancer.

Source: Secondhand smoke @ NHS Smokefree

Image by Challiyil Eswaramangalath Vipin from Chalakudy, India (cigarette.. like a cigarette in the rain) [CC-BY-SA-2.0], via Wikimedia Commons