Ugh, sebhorreic dermatitis...
I have it too, and have suffered since probably the age of 4 or 5 with the itchy patches on my scalp, sometimes itching so bad they would bleed because I scratched so much. Originally about 12 years ago I went to a dermatologist who diagnosed tinea versacolor, and gave me a selenium sulfide prescription shampoo which alleviated it, and stopped the itching of the sebhorreic dermatitis temporarily. The tinea tries to come back once in a while and I use selsun shampoo now to get rid of it before it becomes too severe. However, the sebhorreic dermatitis didn't go anywhere. Since that dermatologist visit, I would still get it on my scalp though not as bad without the tinea versacolor to aggravate it more. More recently, like over the past 3 years, I had started getting itchy flaky areas on my forehead and around my hairline sometimes; the stress of the job I had was causing any little health issue I had to be 3x worse. I went to a dermatologist last year, and she told me it was sebhorreic dermatitis. which wasn't diagnosed with the first dermatologist visit. She prescribed a ketoconazole cream I can apply to my skin anywhere I have a flare-up, and a shampoo which I couldn't get filled because I couldn't afford $140 after insurance for shampoo. I came home and researched sebhorreic dermatitis and found that it is, loosely defined, an allergic reaction to one's own body oils. Adding outside oils, while soothing, makes it worse, as the flakes stick together and are mode difficult to remove, causing less air circulation to affected areas and more irritation. So, I decided to be my own guinea pig: I stopped putting any oil on my hair or scalp for about 2 months. This was in January and I haven't had an episode since, not even on my forehead. After a couple months I didn't like how dry my hair was, so I have made a compromise: I apply an oil, as little as possible, to my hair, concentrating on ends and at least 1/2 inch away from my scalp. This way it doesn't run onto my scalp in the heat or run onto my forehead if I sweat. The first couple weeks I had a couple thick, ugly dry patches on my scalp but they went away. If you try it make sure you use a moisturizing conditioner and style as little and gently as possible until you start adding oil back to your hair, and you should be ok. The key is to avoid putting ANYTHING on your scalp unless it is a prescription, and I don't even have to use my prescription any more. And I suffered with this condition for at least 40 years.