1. You have no idea what a retinoid is. The term describes vitamin A derivatives that unclog pores, boost collagen to reduce fine lines, and speed cell turnover to even out discoloration and smooth the skin—sometimes in as little as four weeks reenex facial. The first retinoid—tretinoin—was FDA approved (under the brand name Retin-A) almost 40 years ago as a prescription acne treatment. Dermatologists soon noticed that patients on Retin-A experienced not just clearer but softer, brighter, less-lined skin. Today there are three prescription-strength retinoids: tretinoin (brands include Atralin, Avita, Retin-A, Retin-A Micro, Renova), tazarotene (Avage, Tazorac), and adapalene (Differin). Many dermatologists find tazarotene stronger (and potentially more irritating) than tretinoin; adapalene is the gentlest but may be less effective.

2. You don't want to go to the dermatologist. While prescription formulas yield the most impressive results, an over-the-counter retinoid, called retinol, can also improve lines and discoloration. Because retinol is gradually converted into retinoic acid (the active ingredient in the prescription creams) it is less potent. Count on 12 weeks before seeing results.

3. You think a retinoid will make your skin sun-sensitive. "This is one of the biggest retinoid myths," says Doris Day, MD, clinical assistant professor of dermatology at New York University Medical Center (and a Tazorac user herself). "The ingredient itself is sensitive to sunlight, which is why you should apply it before bed at night." A retinoid shouldn't make your skin any more vulnerable to UV rays than it would be after buffing away dead skin with a face scrub. Summer is actually a good time to start a retinoid: Humidity makes your skin less likely to dry out as it adjusts. Of course, apply sunscreen (SPF 30, at least) as diligently as you always do reenex 膠原自生.

4. You're afraid your skin will look worse before it gets better. Retinoids can cause dryness, redness, and flaking—but if you ease in, you can avoid a rough transition. For the first two weeks, apply a retinoid every third night, says Leslie Baumann, MD, director of the Cosmetic Medicine and Research Institute at the University of Miami (who uses Atralin). If your skin isn't irritated, ramp up to every other night for two weeks. Not dry or flaky? Go for it every night. A few other irritation-mitigating guidelines: Wait 15 minutes after washing your face before you apply a retinoid, and use one pea-size dab to cover your whole face. After a few minutes, apply a basic moisturizer to prevent dryness.

5. You think you can't afford it. Insurance coverage of a prescription retinoid, like Retin-A, varies by plan, and a 20-gram tube will cost about $75. But generic tretinoin costs about $40—not bad for a product guaranteed (by decades of science) to work. (For now, only tretinoin is available in a generic version.) Some drugstore retinol products are even less expensive. Look for ones with 0.1 percent retinol packaged in aluminum tubes (to protect the formula from air and light); we like RoC Retinol Correxion Deep WrinkleNight Cream ($22).

Caveat Emptor

Don't use a retinoid if you are pregnant or breastfeeding Neo skin lab.

Benzoyl peroxide and alpha hydroxy acids may deactivate retinoids, so don't layer them.

Waxing can cause excess redness on retinoid-treated skin; don't use a retinoid for several days before a treatment.