Getting burned once in a two year time span triples your risk of developing melanoma compared to not getting burned at all. That base level obviously depends on your genetics.
You don't have to be visibly horribly red to be burned. Even just a slight redenning of the skin or it being hot after being in the sun for a while can constitute a burn.
Then let me shift this. If you moved to a location that was completely isolated from the sun, would that cause damage?
That is, I've been assuming there is a spectrum from no exposure to too much. Just as it is with plants. Now, plants obviously need some exposure for photosynthesis. People don't have that, but are there benefits to some base level exposure?
And again, I get the point on burning. And again, that is why I bring up blistering. Something that is obvious in it being bad damage for your skin. Whereas moderate dosing the same behavior could instead give you a callous, which I have never heard called out as bad damage to your skin, though it seems it is a form of damage.
I suppose I am assuming callouses aren't really bad for you? Is that not true?