system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does so much stuff cause cancer?

Everyday I seem to read 'scientists have discovered X causes/linked to cancer'. Why are so many things we eat, use and interact with on a daily basis linked to cancer?
gpt
Cells are always dividing and reproducing.  Many (not all) cancers are caused by a cell having a random mutation that causes them to reproduce much faster out of control.  These cells continue to build up too rapidly until they form a lump, or tumor. 

There is always a low risk of cancer at any time for any cell.  These mutations can just happen. 

When something harms your body by damaging cells, your body reacts appropriately by increasing cell regeneration to heal.  Increased cell regeneration = raising the odds that a cancerous mutation can develop.  

Sustained activity of destroying cells, like regular smoking for many years, keeps your body in a perpetual state of rapid cell growth.  Your body can continue to produce cells too rapidly until one mutates poorly and they develop a tumor. 

In the end, strictly speaking statistically, virtually anything that damages cells in your body can be linked to increased rates in cancer. 

I'll also note here that not all cancers work like this, but many do.