I had problems with psoriasis (or it was seborrhea dermatitis, I never could get an exact answer on what it was) back in the 90's. (it's been gone for at least 12yrs...only notice problems when I'm stressed now)

I used to use a shampoo called T-Gel made by Neutrogena to try to control it. Active ingredient in T-Gel is coal tar. Smells funky, makes your hair feel weird, and if you have any white hairs, makes more of your hair turn white, but when I used it once a week it seemed to work pretty well for me.

I'd put it on my hair and shampoo it in, and then I'd have to wait a few minutes with it in my hair. I'd rinse it out, and sometimes I'd re-wash my hair with regular shampoo after that. (because T-Gel had a weird smell)

I've been meaning to get a new bottle of T-Gel because now with my scalp on the right side being numb (along with the rest of the right side of my body) I dont feel like my hair is getting clean, and it's itchy. Makes me wonder if the problem is coming back. Plus, it kind of strips all the buildup from the regular shampoo out of the hair. Hoping it will make my hair feel cleaner.