Dandruff is common and frustrating, causing flakes, itching, or both. Medicated shampoos with ketoconazole, selenium sulfide, or zinc pyrithione can really help—if you use them the right way.

Seborrheic dermatitis, the rash behind dandruff, is common and often itchy with visible flakes. Medicated dandruff shampoos work well—if used properly.