Ohhh-Ohhh - I left out one nasty - SOY! Most soy comes from GM foods as well - stay clear of soy products - check out what soy is all about by looking up Mercola et al. N-as-sty stuff... (Can even find in many medications, supplements and vits - used a an anti-clogging excipient. No need to use soy, but Monsanto has the world by the short an curlies - larfing all the way to the bank!

I think sebhorrhoeic dematitis is just a skin manifestation of the spondylarthropathies. I've had it on and off for years. Flaky scalp, but only in reddened patches - not all over. If it's raised and nasty enough some might reclassify as psoriatic arthritis.
If I can keep my diet as strict as I can it becomes less obvious and patches on my face become only barely visible. The distribution on my face is usually along the eyebrows, on the upper lip, and just to the side of my nose.

Early on in my disease process I had a number of boils (and two carbuncles) on my scalp - usually secondary to scratching the dermatitis.

Hope you can get on top of it soon.

Good luck - David