They appear more as we get older and some of them may be parasite based. Many of the creams that claim to lighten these spots contain solvents and it is these solvents that are absorbed through the skin, and have the capability to dissolve parasite egg cases, allowing them to hatch and complete their life-cycle rather than being passed out of the body.
I made an industrial strength zapper from a strobe light and a coil. I treated 3 of these spots on my shoulder and neck and within weeks they had dried up and fallen off leaving clear skin underneath. I had another one this year and two weeks after zapping it had gone also. I still have some liver spots and a mole that have been unaffected by zapping.
I do not believe that liver-flushing will eliminate these spots.