A stroll down the skin care aisle shopping for the next big thing that's going to jump start your skin often starts with a lot of excitement, but can quickly unravel to utter confusion. The options are overwhelming. One product that's often a mystery: the serum. What is it? Is it really worth the money? What's the point? Here's some clarity on this high-tech skin booster.

What is a serum?
Think of a serum as the powerhouse of a skin care regimen. "A serum is highly concentrated and has biologically active substances to help accomplish specific goals," says Catherine Orentreich, M.D., a New York City-based board certified dermatologist who serves as a guiding dermatologist for Clinique. Packed with potent and targeted ingredients, serums are generally on a single mission, whether it's to reduce dark spots, boost your glow, smooth fine lines or tighten everything up a bit. A serum is also lighter and thinner than most moisturizers, which allows it to quickly penetrate into the skin and work on a deeper level. It's the stealth bomber of skin care.

Do you need a moisturizer and a serum?
Not really if you don't have any big skin gripes that are bugging you. But, if you're bothered by a skin concern, like a relentless dark spot or little lines creeping up around your eyes, then adding a serum to your regimen is a good idea. Using a serum and a moisturizer that contain complementary ingredients to tackle an issue is like delivering a one-two punch to knock it out. You'll see results faster. Together, they're the ideal support group for your skin.

If a serum is more powerful than a moisturizer, do you even need a moisturizer?
In addition to all the potent problem-solving ingredients that are in a serum, it may provide a certain amount of hydration, but not enough to replace your moisturizer. Moisturizers also deliver a more well-rounded meal, containing other healthy ingredients that your skin needs beyond battling your primary concern. Lastly, serums don't have SPF because they are designed to go deep into your skin, while sun protection ingredients are supposed to stay on the upper layers to deal with those harmful UV rays.

Which do you apply first?
The rule of thumb when it comes to layering skin care: go from thinnest to thickest. Serum first, moisturizer second. You can use the same serum morning and night, but use a day cream with SPF and a night cream with more skin-repair ingredients.

When should you start using a serum?
It's not really about age, but the condition of your skin, and if you have any issues that you want to tackle. Thinking you need a power pair? Here's what to look for...

If your concern is...dark spots and uneven skin tone
Start with a serum like Even Better Clinical Dark Spot Corrector & Optimizer, which contains Vitamin C, yeast and salicylic acid to break up dark spots and reduce discoloration while soothing Gyokuro green tea, a potent antioxidant, quells irritation. "Salicylic acid is wonderful for promoting exfoliation," says Dr. Orentreich. Pair it with Even Better Skin Tone Correcting Moisturizer Broad Spectrum SPF 20, which contains similar ingredients, plus SPF to prevent future damage.

If your concern is...tightening and toning
While the passing of time is inevitable, sagging isn't. As you age, the support structures that give your skin its cushion and bounce start to break down. To fight this loss, look for ingredients like collagen, elastin and peptide, which support your skin's structures, helping to bring back youthful-looking contours to your face. Sculptwear Lift and Contour Serum for Face and Neck can create a visible 40% lift along the jawline in eight weeks. To support that hardworking serum, Repairwear Uplifting Firming Cream Broad Spectrum SPF 15 contains protein and peptide to help firm, volumize and tone skin. It also provides protection against UV rays, which actually can break down collagen. Give your skin a little workout by applying it using this stimulating, facialist-developed massage technique.

If your concern is...lines and wrinkles
Don't let fine lines and wrinkles cause you anxiety. Keep calm and slather on this powerful pair: Repairwear Laser Focus Smooths, Restores, Corrects and Repairwear Laser Focus Line Smoothing Cream Broad Spectrum SPF 15. Packed with amino acids and peptide to help rebuild skin's natural support system, while also exfoliating away dead surface skin, the serum is likened to an in-office wrinkle reducing laser treatment. When the #skingoal is to minimize lines and wrinkles, the right moisturizer plays a uniquely important role. The more plump your skin, the less deep your wrinkles look.

If your concern is...a little bit of everything!
Oh, to only have one skin care concern. For many of us, it's sagging and dark spots, or wrinkles and dullness. Fortunately, some serums are smart enough to multi-task. Clinique Smart Custom-Repair Serum intuitively understands the needs of your skin and provides custom repair, whether you're aware of the damage or not. And a smart serum needs a clever moisturizer.>Clinique Smart Broad Spectrum SPF 15 Custom-Repair Moisturizer does a lot of everything: It tackles lines and wrinkles, lifts and firms skin, evens skin tone and improves radiance. This moisturizer has a healthy dose of hyaluronic acid, which can hold 1,000 times its weight in water, plumping up your skin, while also delivering ingredients to visibly repair damaged skin.

Photo: Yasu + Junko | Words: Kristen Bateman