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 is the rash that causes dandruff. It is common and annoying, causing itchiness or visible flakes or both. Medicated dandruff shampoos really help, if you know how to use them correctly.