Turns out washing your head with shampoo twice and blow drying afterwards fixes my itchy scalp. Don’t ask me why, I don’t know. I just know that since my hairdresser did that, I feel so much better.
Thought I’d spread the word, because it is so frustratingly simple :D
Also Sodium lauryl sulphate , SLS or Ammonium lauryl sulphate. These detergents define most shampoos. They strip natural oils then replace the oils with silicone.