All I recall besides being one of many carcinogens is that it's in cigarette smoke. From a Dutch health page. [https://www.rivm.nl/en/tobacco/harmful-substances-in-tobacco...]

> For smokers, tobacco smoke is the most important source of exposure to benzene. It is released in the smoke when tobacco is burned. Non-smokers are also exposed through tobacco smoke when they inhale smoke passively. A typical smoker inhales an average of ten times more benzene per day than a non-smoker.