★★★★★
I also tried an alkaline diet without any success until I read about FODMAPS. Now I focus on primarily greens for veggies, skip all nightshades, and rarely eat any fruits or veggies containing FODMAPS and my skin is getting better.
I have seen the most relief from the use of ACV and green juices as well as from raw broccoli (which is very high in vitamin E, thus nourishing the skin). As for topically, ACV may burn for a bit, but I refuse to wash it off and it does make things better, however, is not a magic potion (bummer).