I've had issues with dandruff for years. Head and Shoulders and Selsun Blue and others would help but I'd still itch. In the past few years I've kept my hair very short since it cuts down on the itching.
Now for some science:
Dandruff is caused by a yeast/fungus that feeds on the oily secretions of the scalp. The oils are secreted by the sebaceous glands to keep hair healthy. Quoting wikipedia from a 2006 paper: "[the yeast] metabolizes triglycerides present in sebum by the expression of lipase, resulting in a lipid byproduct oleic acid (OA). Penetration by OA of the top layer of the epidermis, the stratum corneum, results in an inflammatory response in susceptible persons which disturbs homeostasis and results in erratic cleavage of stratum corneum cells."
Now for hypothesis:
Certain fungus are known to secrete anti-bacterial compounds; this is where we get penicillin from. So, why would M. globosa create oleic acid when metabolizing its food? Perhaps to kill off or reduce the bacteria on the scalp that would compete with it. So neutralizing the acid could be a two-fer: it will directly help with the itching. Also, it may allow competing bacteria to grow in larger numbers. How can we reduce the acidity of the scalp? With a baking soda rinse.
So I've been washing my hair with nothing but baking soda for the last few months, and my dandruff problems are much reduced. My scalp itches a lot less, and I'm growing my hair out for the first tie since 2004. I can feel a difference when I skip the baking soda for a few days.
Also note that baking soda does not strip any of the natural oils off the scalp and hair, so things like conditioner that restore all the goodness that shampoo just stripped are also not necessary.
It's not a flashy cure, it costs practically nothing, and it's not instant. And no for-profit company would ever spend the money for a study to confirm that a baking soda rinse helps dandruff, because then they couldn't sell the much more expensive, and less useful, dandruff shampoos.