system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a healthy cell sometimes produce a cancer cell

An healthy cell keep dividing until it is no longer needed. A cancer cell is a cell that uncontrollably keeps dividing itself.

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How does smoking, asbestos, radiation, UV light, processed food etc. affect the normal process and make a healthy cell produce a cancer cell?
gpt
So every time your cells divide, they need to make a copy of the DNA in the cell. This process isn’t full-proof though, and errors can happen. These errors usually don’t cause problems, since small errors might not make any difference to how the cell operates. The problem comes when too many errors start to occur and the cell completely malfunctions. Your body can sometimes recognize this malfunctioning cells and get rid of them, but sometimes these cells multiply too fast or are able to hide themselves from being destroyed. 

Radiation, smoking, chemicals, and a lot of other things can cause more errors to happen in your DNA.