I read your answer to another problem that dandruff is caused by exposure to the elements i.e. the sun, UV rays, etc. I don’t buy this or else similarly situated people would have the same amount of dandruff.
We are all different and we manage our skin differently. Dandruff is caused by the accumulation of dead skin cells on the scalp, often in dry scalps. There are good shampoos for this and I would suggest that you try them serially until you find what works for you.