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
It possibly depends on hair type - my solution was “don’t use shampoo with Sodium Laureth Sulphate” in it.
I had the opposite problem. I had some hippy shampoo that caused so much dandruff that it turned into scabs. As soon as I started using ordinary shampoo again it was fine.
…but foamy toothpaste with too much SLES gives me ulcers. I have to avoid the common supermarket brands.
Also Sodium lauryl sulphate , SLS or Ammonium lauryl sulphate. These detergents define most shampoos. They strip natural oils then replace the oils with silicone.