My scalp itches constantly, has done so for years.  I've seen two
dermatologists, and they tell me that just by looking at the skin,
they can't see anything wrong.  One guy said, "Some people just itch
on part of their body for no reason."  They did try me on various
shampoos:  Zincon, T-Sal, T-Gel, Capex, Loprox, Nizoral, and
Clobetasol Propionate.  None of them have helped significantly.  Have
also tried regular anti-dandruff shampoos of various brands.  One
dermatologist wanted to try me on some stuff that was based on urea,
but I draw lines someplace.

Anyway, I actually read something recently that tiny little bugs
(mites, or something) can cause itching, but you would think this
would cause some visible symptoms that the dermatologists could see
and diagnose.  Does anyone have any thoughts, and any suggestions for:
(a)  Possible diagnoses I could suggest to the doctors (you'd think
they wouldn't need help, but maybe they do), and...
(b) Suggestions for other shampoos to try?

FWIW, the itching seems to get worse in the evening, and I find myself
scratching a lot at night.

I also use hair dye (Just for Men), and Minoxidil, but the problems
with itching long pre-date the use of the either of those.

Thanks in advance for all replies.

Steve O.