With news that most Americans are deficient in the "sunshine vitamin," some medical experts advocate exposing skin to UV rays for 15 minutes or so daily, sans sunscreen. But unprotected exposure only helps your body make enough D when several variables—time of year, time of day, location, and skin type—work in your favor, according to a 2010 study. Also, because UV exposure can cause skin cancer and premature aging, it's wiser to take supplements, says Amy Wechsler, MD, author of The Mind-Beauty Connection (Free Press, 2008).

Beauty fix: Protect skin at all times, applying sunscreen to every exposed body part, including the neck and hands. Choose a broad-spectrum SPF 30 product that physically blocks UVA and UVB rays with zinc oxide or titanium dioxide, rather than harsh chemicals. The nanoparticles used in some mineral-based sunblocks to avoid the "white-face" effect and more effectively block UV rays pose little threat when applied topically, according to the Environmental Working Group. But avoid them in aerosol form, which increases risk of inhalation, an immune system concern, says Logan. The latest: Companies are reformulating with non-nano zinc that offers a similar consistency. For facial sunblocks, look for non-comedogenic or oil free on labels to avoid breakouts.

Try: Badger SPF 30 Sunscreen (non-nano); Elemental Herbs Zinc Sunstick SPF 30; Marie Veronique Organics Moisturizing Face Screen, Light Tint, SPF 30