What does a UV camera reveal about sun-damaged skin

Factual Questions
1

Interesting video here showing what people look like in normal lighting, and in the UV spectrum. (Keep watching to the end for a dramatic demonstration of the effectiveness of sunblock.)

The claim (which I’ve heard before) is that the UV image reveals sun damage that can’t be seen by normal visible light, with the damage manifesting as a blotchiness, almost like a dense pattern of freckles. But it’s never explained what we’re seeing. A couple of questions come to mind:

-Why does sun-damaged skin appear freckly under UV light? Is the damage unevenly distributed?

-what does a change in UV reflectance/absorbance indicate? IOW, what is it about UV-damaged skin that changes its reflectance/absorbance?

2

Here’s an actual study on the topic. I don’t have the time to see if it properly answers your questions, at least not right now, but I’m sure it’s a good start.

Sun damage in ultraviolet photographs correlates with phenotypic melanoma risk factors in 12-year-old children

3

It all depends on whether the video was made by medical researchers or people trying to sell miracle sunblock/cosmetics.