system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Carcinogens; How Do They Work?

I understand that cancer is an uncontrolled growth/replication of benevolent cells, but how do carcinogens cause/increase the chances of getting cancer?

As an addendum, what makes some people more susceptible to getting cancer. My great aunt smoked from the age of 12 to the day she died of advanced alzheimers at 92, and never had any kind of cancer. On the other hand, my friend never smokes anything, and doesn't hang around smokers, yet he developed lung cancer at 25. Why?
gpt
Carcinogen is a very broad term for agents which can damage your DNA, it encompasses all sorts of things from reactive substances to different types of radiation.

When a carcinogen reaches a cell and manages to hit your DNA, one of several things happens. If you're lucky, the DNA is repaired fully, which is the case most of the time. If you're somewhat lucky, it's repaired in the wrong way but the change doesn't matter and the cell lives on as per usual. If you're somewhat less lucky, the change is severe and the cell can no longer sustain itself and dies - not that it matters when you have billions upon billions of identical ones.

If you're _extremely_ unlucky the damage occurs in such a way that the cell "forgets" that it's supposed to stop replicating, resulting in the uncontrolled growth you mentioned.

As for why your grandmother didn't get cancer, the answer is most likely "dumb luck". It is possible that there are some genetics involved too but the mechanics behind those are likely beyond our current understanding.