UV exposure prompts the skin's pigment-producing cells to work overtime, and over years that shows up as sun spots, age spots and a generally uneven tone — sitting at different depths depending on how long the damage has been building. It also affects texture and collagen, which is why sun-damaged skin often looks rougher, not just darker.
Treatment works in stages that match the different depths involved. Laser targets pigment directly, encouraging spots to darken briefly before flaking away over the following days to reveal clearer skin beneath. Resurfacing and skin-quality treatments work alongside it to even out tone and texture more broadly.
The honest part: sun damage can't be undone at a cellular level — what treatment does is reduce the appearance of it, session by session. The single biggest factor in how long that improvement lasts is what happens afterwards: daily SPF, because new damage will form on unprotected skin regardless of what was treated before.