Q. So many products claim to get rid of undereye circles. How do I know which one to buy? 

A: If your complexion is fair, your (red or purplish) dark circles are probably caused by blood vessels just below the skin. If you're olive or darker, your (brown) circles are probably caused by pigmentation. Look closely in a mirror, and press on the skin; if the color decreases, your circles are more likely from blood vessels, says Heidi Waldorf, MD, associate clinical professor of dermatology at Mount Sinai School of Medicine in New York City. In this case, you might consider treatment with the V-beam laser, which zaps the vessels, causing them to disappear. For pigment-related shadows, Waldorf typically starts with creams containing retinoids (prescription tretinoin or tazarotene or over-the-counter retinols), to reduce pigmentation and increase cell turnover, and hydroquinone, a bleaching ingredient. Other helpful ingredients to look for are kojic acid, alpha hydroxy acids, kinetin and azelaic acid.

Keeping the area well hydrated can improve the appearance of either kind of undereye shadow and make it easier to apply concealer; use eye creams containing glycerin, petrolatum, dimethicone or kinetin. Gels containing caffeine will temporarily tighten the skin, too, Waldorf says. If topical creams seem to irritate the area or make the circles worse, or if the skin is burning, itching or scaling, see a dermatologist. The cause of the darkness could be eczema, for which you may need a prescription topical anti-inflammatory cream.

Keep in mind: First figure out what's causing your undereye shadows; creams can reduce only the pigment-related type.

Keep reading: 4 steps to conceal undereye circles

Q. My face is always shiny even though I use blotting papers and powder. Help! 

A: "This can be a challenging problem," says Jeannette Graf, MD, assistant clinical professor of dermatology at Mount Sinai School of Medicine. But you already know that. Graf suggests using a cleanser with witch hazel, and following it with a lotion containing oil-absorbing microsponges. Next, try applying a foundation primer—the silicone in it gives your skin a matte finish—wherever you get shiny (on your forehead, say). Then, over an oil-free foundation or tinted moisturizer, use a brush to apply a veil of loose powder (don't use your fingers; they can transmit oil).

Keep in mind: Avoid drying out your skin, since that can cause oil glands to go into overdrive.

Keep reading: Val's basics for a fresh and flawless look

Q: Come on, do I really need an SPF if I'm inside all day? 

A: Say you're in your office, sporting a vintage midnight blue Yves Saint Laurent velvet jacket with silk lapels. It starts to rain. Will it kill you to go out without an umbrella? Of course not, but you won't be doing your jacket any favors. Now, if you think of your skin as a commodity at least as valuable as a vintage bolero—and I know you do—you'll apply a similar kind of reasoning to your face. Getting to work, dashing out for a salad midday and going home all expose your skin to damaging UVA/UVB light, says Brad Katchen, MD, founder of SkinCareLab in New York City. And UVA rays, which cause premature aging of the skin, are transmitted through glass, so if you're lucky enough to have an office with a window, you may be getting a daily sunbath at your desk. Using a moisturizer with SPF is an easy way to apply protection.

Bottom line: You probably get more sun exposure than you think, so use an SPF 15 lotion even if you spend most of the day inside.

Keep reading: 7 never-fail sunscreens

Q. My moisturizer has an SPF 20. My foundation has an SPF 15. Am I getting a combined protection of SPF 35? 

A: I understand your thinking on this, but, no. You're getting only the highest SPF protection you wear.

Keep reading: Why would you want an SPF 100+?