I have itchy scalp from time to time, more so in the winter, accompanied by flakes despite the fact that my scalp tends to be oily! Dandruff shampoos never help; tea tree to some extent, but not completely. The one thing that really helps is this:
4-5 drops rosemary oil
1/2 TBSP olive oil
Mix in hands and massage into scalp before bed. Cover pillow with towel to protect pillowcase. Wash out in a.m.
Use up to 4x per month.
The last time I did this was a few weeks ago. My scalp was SO itchy (and flaky), I used double the recipe (10 drops + 1T) to make sure my entire scalp was saturated. It felt SO much better when I woke up in the morning! Used a low poo to wash out all the oil. I'm currently using the MGA shampoo and this helps as well, but the rosemary/olive oil overnight treatment is my secret weapon.