Hyaluronic acid is a moisturizing workhorse. The molecules hold onto water better than just about everything else, and they help keep your skin moisturized for hours. In addition to finding them in creams, lotions, and serums, hyaluronic acid is also used in injectable fillers like Restylane. The FDA determined it was safe largely because we all have it in our bodies anyway (think: areas that need a lot of lubrication, like joints).

If you have a dry scalp or dry hair, hyaluronic acid adds moisture and it helps your hair hold onto moisture until you wash it again. John Masters Organics Bare Shampoo, $14.50, contains hydrating jojoba oil, as well as hyaluronic acid. To protect your hair from heat styling, try Phytokeratine Repairing Thermal Protection Spray, $32. And if you're looking for more volume, check out Oscar Blandi Hair Lift Instant Thickening and Strengthening Serum, $30, which also contains rice starch powder to make your hair look fuller.

First things first: there are two types of stem cells. Human-derived and plant-derived. Human stem cells carry a host of ethical questions, plant-derived stem cells may not do much at all (depending on which expert you talk to). However, if they're doing what they're supposed to do, both varieties of stem cells trigger your skin cells to regenerate more quickly and act like younger cells.

According to biologist Paul Knoepfler at the Univeristy of California Davis School of Medicine, eventually stem cells will be used to cure baldness. "Research on specialized stem cells that can grow hair has been advancing at a rapid clip," he says. But we're not there yet.

In the meantime, products like Julien Farel Restore, $33, contain plant stem cells, hyaluronic acid, and antioxidants to protect and hydrate the scalp and help you grow healthier hair.

Good old salicylic acid -- you probably know it well. It's one of the two over-the-counter ingredients approved by the FDA to treat acne (the other is benzoyl peroxide), which means it's in half the breakout-fighters on the market. What you might not realize is that it comes from a natural source -- willow bark extract -- and that's it's a fantastic exfoliator.

In hair care products, it works in a similar way. It removes built up product that sits on your hair (making it look dull), as well as your scalp (making it itchy, and hindering your hair growth).

Look for it in Yes To Carrots Scalp Relief Shampoo, $7.99, Jason Thin to Thick Revitalizing Scalp Elixir, $9, and (no surprise here) Dr. Gross Root Resilience.

Ceramides are lipids (a form of oil) commonly found in skin care products designed for sensitive or eczema-prone skin. They create a protective barrier, helping the skin hold onto moisture while protecting it from the outside world -- things like pollution and other irritants.

If your hair is prone to breakage or splitting, ceramides coat the hair shaft and reinforce it like scaffolding. Try Kérastase Fibre Architect, $42, before styling -- it fills in holes and strengthens each hair strand. If you're looking for a deep treatment, there's Biolage Color Care Cera-Repair Pro, $35.

When people see collagen in skin care products, they get excited. Plump, young looking skin can generally be attributed to layers of collagen underneath the surface. The collagen in skin care products doesn't actually penetrate the skin, but it does hold onto a lot of moisture. Similar to hyaluronic acid, it can help keep your skin hydrated for hours.

Collagen works the same way in hair care products -- it helps your hair and scalp hold onto moisture while making your hair look thicker and fuller. Try Sally Hershberger Collagen Volume Shampoo and Conditioner, $9 each, or Organix Thick & Full Biotin & Collagen Shampoo, $6. The Dr. Gross Root Resilience line also contains collagen.