You have not mentioned your age. It is not infection but endocronological problem. You have to avoid fatty foods and take adequate fluids. Massage
with non oil based solutions. Alternately put two spoons of yogurt in two spoons of sarsoon oil and massage your scalp with this solution and comb your hair. Keep it for two to three hours and take bath. Only wash your head with water and comb your hair so that all the existing dandruf is removed. Try it every alternate day and see the result but maintain the diet as advised. (excerpt from alternative medicine).
You can also give a trial with Head and Shoulders shampo.