Question: How can someone get cancer if it's not contagious?

Ciarán O'Brien answered on 11 Nov 2014:

You can get cancer if you handle dangerous chemicals or if you’re exposed to an unhealthy does of radiation (small doses like getting an x-ray at the hospital are fine, your body can shrug that off). Some unlucky people are born with genes that might just go nuts and cause cancer anyway.

Cancer is when the cells of your body start growing out of control. All cells grow and divide regularly, but they know not to do it all the time. With cancer, something changes in the cells and they forget that they’re supposed to rest in between growth sessions. They divide all the time, and your body can’t bring them back under control. Depending on where in your body that happens, that can be really dangerous, but sometimes it’s actually harmless.

The reasons someone gets cancer are to do with the DNA in their cells. Normally it works fine, and the cell uses it as a blueprint for making proteins and repairing itself and deciding when to divide. But some chemicals can damage or even mutate our DNA, and if certain parts of our DNA get damaged, it can cause the cell to forget how to behave, and it becomes cancerous.

Some people have DNA that COULD cause cancer, but normally doesn’t because the rest of the cell keeps it under control. But given the right set of conditions, the cancer-causing genes can sometimes ignore the rest of the cell and go haywire.