I've had seborrheic dermatitis for over 6 years now - My entire face would be covered in scaly patches. There is no cure but you can treat it and keep it minimized in its intensity.
By far and away the most helpful thing I've found in my battle against SD is salicylic acid - The strongest over the counter percentage is 3 percent - this helped me but was not enough. My doctor prescribed salicylic acid at 6 percent prescription strength and that applied twice a day keeps it mostly under wraps. Once or twice a year it flares up despite the salicylic acid cream, usually at the beginning of summer and winter - at these times I use a lot of apple cider vinegar and sulfure masks in addition to the prescription strength salicylic acid cream.