system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5: How does smoking cause cancer?
gpt
Chemicals in tobacco cause damage to the DNA in cells in the body. These cells then divide into other cells with a higher number of mutations then they would have without the damage. The higher the number of mutations the greater the risk that one of those mutations will cause the cell to become cancerous. 

Every time your cells divide your basically playing a cancer lottery with relatively low odds. Certain environmental factors increase those odds, tobacco smoke is one of them.