How can things like sunburns and smoking still increase risk for cancer decades after their damage has been done to the body?

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How can things like sunburns and smoking still increase risk for cancer decades after their damage has been done to the body?

In: Biology
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Cancer is basically a copy-error in a cell mutating into a big problem. Nearly every cell that has to split to recover from an injury can end up with thay issue (and I only use the word ‘nearly’ to avoid some smartass coming up with an example I didn’t know about). The more the cells divide like that, the older the cells are. The older a cell is, the more likely it is to lead to cancer on mitosis (cellular division).

This isn’t a comprehensive explanation, but it’s as simple as I can keep it, without failing to answer the question.

Imagine you’re building a brick wall. At some point you used some faulty bricks, but then you finished up the wall with solid bricks and it’s standing fine, those faulty bricks weren’t a major problem. At some point in the future, some of your good bricks get damaged. Normally it wouldn’t be a big issue, but it happened to be right around where those faulty bricks were and now the structure is too weak in that spot and the wall collapses.

Smoking/UV radiation damages DNA, the building blocks of your cells. In much the same way, that initial damage might not cause cancer, but the damage persists throughout your life and makes any future damage more likely to cause cancer.

Cancer is cumulative (genetics + environment). Smoking or sun exposure does damage but may not be the final cause of cancer but contributes.

UV rays, wich causes sunburns, and certain components in tobacco smoke cause damage to the DNA. If DNA gets damaged, it is like a scratch on a CD and information (aka building plans for all the stuff your body is made of) are not read correctly. Those replication errors happen all the time, but normally the replicated cell realizes that it is a potential danger for the organism and requests a bullet to the head (that is called programmed cell death or apoptosis).
But that is not the only safeguard, your DNA contains structures called telomeres. Telomeres are long strands of basically monotone nonsense, they do not contain any useful information. Their job is it to stabilize the chromosome (that is how DNA arranges itself. Those telomeres are not infinite though, they are like a sacrificial protector. With time, they get shorter and shorter. Or damaged, like through toxic fumes or high energy radiation (like UV). The shorter they get, the less protection the chromosome has. So when I smoke like a badly tuned bbq through my teenage years and 20s, I destroy more telomere than what just getting old would. So the protection could be used up by the time I would be 45 instead of 105.
Even when I stopped smoking at thirty, the damage is already done.