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
I stopped using shampoo on my (short) hair over 15 years ago as well, no issues.
There’s a subreddit for this, called nopoo. Not kidding.