>>14229044yeah, skin aging still happens from just getting old
UV damage, like from the sun or welding or whatever, causes your DNA in skin cells to covalently bond. two thymine (or two cytosine) bases next to each other will bind to each other and this fucks up your DNA structure. most of this is fixed practically instantly, but until it's fixed, that part of the DNA is unsuable for cellular machinery (like dna polymerase).
usually, this is fine and gets fixed. the thymine-thymine adducts are fixed correctly most of the time.
the problem is that if there's a cytosine involved (like a CC or CT adduct), then often the cytosine is converted into thymine, and now you've got an incorrect match when it gets fixed.
so when that is repaired, there's a 50/50 chance that your cell picks the correct strand to use as the template. it either cuts the side with the "wrong" base (the side with the C converted into a T), puts on the correct base using the other strand as a template, and you're back to normal.
or it cuts the "original" side, and now you've got a mutation in the genome.
