How to know if i have dry scalp or dandruff?

Treat for Dandruff : See Dermatologist. Dandruff is associated with malassezia fungus infection. Try over-the-counter dandruff shampoos, and look for one that contains zinc pyrithione, which can reduce the fungus; selenium sulfide, which can limit cell turnover and decrease the amount of fungus; salicylic acid, which works as a scrub to slough off dead skin; or ketoconazole, which works against a broad array of fungi.

Try it: Easiest answer is to try dandruff shampoo over the counter. If no improvement see a dermatologist.