Skincare SOS: When Do You Need a Doctor?

If You Have Constant Flaking and Drying

Hit the drugstore. Your cleanser may be stripping the top layer of skin, says Heidi Waldorf, MD, a dermatologist in New York City. Switch to one that locks in moisture with lipids and proteins. Try Cerave Hydrating Cleanser ($11.99, drugstores).

If You Have Cystic Acne

See the derm. Has the occasional blackhead turned into bouts with red under-the-skin bumps? A doctor's arsenal of oral antibiotics, hormonal treatments, and corticosteroid injections can help prevent long-term scarring.

If You Have an Old Acne Scar

Hit the drugstore. To help fade a scar, boost skin-cell turnover with a cream with retinol, like Vichy LiftActiv Retinol HA SPF 18 Total Anti-Wrinkle Renovating Care ($46, drugstores). Be patient: It can take several months to see results.

If You Have Ruddy Patches

See the derm. Constantly flushed cheeks can be a sign of rosacea, a skin disorder resembling adult acne that can be treated with a regimen of oral meds, prescription gels, and azaleic acid-pumped topical creams, like Finacea.

If You Have Supersize Pores

Hit the drugstore. "Pores worsen when hair follicles clog with oil," Dr. Waldorf says. Clean & Clear Advantage Blackhead Eraser Exfoliating Cleanser ($19.99, drugstores) combines salicylic acid with a vibrating pad to slough off dead skin.

Originally published in FITNESS magazine, February 2010.