Which shampoo is best for stopping dandruff? —G.B., Ossining, N.Y.

It varies by person, since different shampoos target different causes of dandruff. As a first choice, try a product containing pyrithione zinc (Head & Shoulders) or selenium sulfide (generic, Selsun Blue), which attack excessive skin growth on the scalp—a possible cause of dandruff—and are the least irritating to the skin. If that doesn’t help, consider a shampoo with ketoconazole (Nizoral A-D), which combats the fungus P. ovale, another potential source of dandruff. If the problem doesn’t improve after about two weeks, try a more potent, exfoliating shampoo containing sulfur (Maximum Strength Meted, Sulfoam) or salicylic acid (P&S, Scalpicin, X-Seb), which can help loosen up and clear away dead, flaky skin.