Dandruff and seborrheic dermatitis both seem to result from a reaction to yeast that normally live on the skin. You CAN control Malassezia!
Soaking the hair in old-fashioned amber Listerine before washing it can often alleviate an itchy scalp. The herbal oils in Listerine discourage skin yeast.
Herbal oils in household products as well as herbal teas can be helpful in controlling the itch and flakes of dandruff.