Have you ever tried a shampoo without sodium laurel/laurteth sulfate? Some people (myself included) have a sensitivity to these ingredients that are in most shampoos, and they can trigger dandruff. Most of the anti-dandruff shampoos have high quantities of one or both of them. It might be worth trying one of these as well as the anti-dandruff shampoos. They will not be sold as anti-dandruff (that I've seen), but will be with the more "natural" products most of the time. Most of the shampoo bars will work for this as well.
I never had a problem with lots of flakes, but I could get some major itchy scalp, and since switching to non-SLS/SLES shampoos, it has all cleared up.
YMMV
James
I've had the same experience. I tried every anti dandruff shampoo on the market with no help. I only had flakes in the winter...not even sure if it was actually dandruff. The biggest problem was my itchy scalp. It was maddening. Almost immediately after buying a shampoo without SLS my problems were gone. Its a pretty common problem and there are more and more shampoos without SLS coming onto the market.