Hey jblake,I have dermatitis really bad. In fact, it is the main reason I started buzzing my hair down pretty short to begin with about two years ago, as any time I would let my hair grow out, it seems that immediately I would start to get red and flaky all over my scalp - along with my beard and eyebrows. I tried all the different types of over-the-counter dandruff shampoos, and none of them were fully effective.Once I started shaving completely, I've found that all my dandruff problems have vanished for the most part (but even with a couple days of growth, the flakes seem to come right back).It's winter, and so dryness is just part and parcel of the problem, so make sure you keep your scalp lotioned up.If you are wanting to razor shave your head completely and are concerned about the built up flakiness, here's what I did: use your hair trimmer with no guard, then use an exfoliant srcub of some sort to get all the flakes out and loosened. From there, it should just be a matter of shaving as normal.
I find that a shaved head and plenty of fresh air and sunshine helps a lot.