Liquid nitrogen (cryosurgery) is used for a lot of different purposes in dermatology including, sometimes, removing brown spots. It does work! There are problems with it though when used for cosmetic purposes because it often leaves a residual white spot or small scar which can be as annoying as the brown spot was in the first place. I still use it with my patients sometimes very lightly, when there is a resistant lentigo (flat brown spot) or an early benign keratosis (raised brown spot that’s not precancerous). We often then use a laser also to really get the skin color uniform. Many dermatologists who do cosmetic work will use combinations like this.
In my opinion, using liquid nitrogen alone doesn’t work well because the whole goal cosmetically is to get the skin’s color very even again, and you really can’t do that just spot treating. Hope this helps. Dr. I