No. Dermatologists recommend that you wear sunscreen every day—even if you step outside for only a few minutes to grab lunch or catch the bus.

The problem is that many makeup sunscreens block only skin-burning UV-B rays—not the deeper-penetrating UV-A rays, which contribute more to wrinkling and skin cancer. So if you walk at lunchtime or simply sit near a window for hours—UV-A rays do pass through glass—use only real sunscreen with an SPF of 15 or greater under your makeup, says Debra Jaliman, M.D., a dermatologist and clinical instructor at Mount Sinai School of Medicine in New York City.

And be sure the label says "broad-spectrum," which means it blocks both UV-A and UV-B rays and contains ingredients such as zinc oxide or titanium dioxide. Also consider sunscreens made with avobenzone (Parsol), which may be the most effective UV-A blocker yet.