Your Healthiest Hair Ever

"Healthy hair looks shiny because its cuticles are smooth, creating an uninterrupted surface of light along each hair fiber," says Jeni Thomas, PhD, senior scientist for Pantene. Dullness indicates that the cuticle, or protective layer, has been damaged (common culprits: washing, brushing, and coloring). Adding insult: A ragged cuticle is likely to prompt frizz.

TEST: Have a friend take a picture of your hair while you're outside. Does the sunlight reflect evenly off your strands? If not, use these strategies.

Find a Gentler Shampoo
Traditional sudsing agents -- sodium lauryl and laureth sulfates -- can be too drying. Instead look for a cleanser (such as L'Oreal Paris) made with ingredients like decyl glucoside, which pulls away debris without stripping hair.

Be Cool
Warm water opens the hair's cuticle, allowing shampoo to get inside. Conditioner, however, is best rinsed with cold water, which seals the cuticle, says Rodney Cutler, a salon owner in New York City and Miami. When blow-drying, finish with the cool-shot button. This not only reseals the cuticle but also allows you to detect still-wet spots (they'll feel super chilly) -- important, as they can cause dulling frizz. (Blow-dry strands with hot air again, then top off with cool.)

Comb in Conditioner
Moisturizing styling products, such as leave-in lotions and sprays, prevent dryness and seal the outer layer of hair. But it's important to comb them in. "When the product is not evenly distributed, the bare patches look dry and lackluster," says Cutler. Choose silicone-free products (such as Living Proof No Frizz Styling Sprays, $24, sephora.com). Otherwise, the clingy ingredient can be difficult to remove with shampoo, leaving behind a dulling film.