When you're faced with stubborn dandruff that just refuses to go away with other dandruff shampoos, it's time to call on ketoconazole, the king of scalp antifungal agents. Ketoconazole treats a number of different types of fungal and yeast infections and is usually the ingredient used in prescription dandruff shampoos. You can find the active ingredient in OTC anti-dandruff shampoos, like Nizoral A-D Shampoo, $16.99.

Tea tree oil, from the Melaleuca alternifolia plant, is an ancient remedy for acne, athlete's foot and lots of other infections. Plus, research suggests that its fungus-fighting action may treat dandruff. If you don't find tea tree oil too strong, you can rub it directly into your scalp, let the oil sit for a few minutes and rinse well. Or, look for a dandruff shampoo that contains tea tree oil, such as Aubrey Organics Tea Tree & Primrose Shampoo, $14.98. This shampoo not only includes tea tree oil to fight fungus, it contains primrose oil to moisturize your dry scalp.