Could seborrheic dermatitis be linked to a food allergy? Is the body mistakingly attacking itself? No fam history, think dairy is the prob.

No. It is considered to be from an reaction to overgrowth of an usually innocuous resident fungus on most adult skin (Pityorsporum orbiculari) especially when the skin is oily. Twice weekly topical antifungal agent often works well.
Yes,unknown,possible. While not widely accepted, food allergies can aggravate seborrheic dermatitis and dairy seems to be the most common food associated with it. It is more common in those with autoimmune disease but it is not definitely known if it is an autoimmune disease- its cause is still not known! See