6 Shiny-Hair Saboteurs

The saboteur: Your shower. Sediment from your showerhead is damaging. "Mineral deposits and rust in your pipes dull hair like nobody's business," says colorist Kyle White of the Oscar Blandi salon.

The savior: Vinegar. Twice a week, add one teaspoon of apple cider vinegar to a cup of water and pour it over your hair after shampooing and conditioning. Wait five minutes, then rinse. The citric acid "removes all the mineral buildup," says White. For a speedier, less smelly alternative, Fekkai Apple Cider Clarifying Shampoo gets out the gunk in a single step.

Shopping: Fekkai Apple Cider Clarifying Shampoo

The saboteur: Careless conditioning. If you rinse off conditioner seconds after you apply, you may as well have skipped it altogether—the proteins and lipids need time to penetrate the tiny holes and fissures in the hair shaft, says Teca Lewellyn, a P and G beauty scientist.

The savior: Patience."Your conditioner­ can be thick or light—none of them hydrates instantly," says Lewellyn. Leave it on for "two whole minutes," says Mara Roszak, a celebrity hairstylist for Starworks Artists. "It may seem like an eternity, but that's how long it takes to hydrate hair, especially the ends." For fine hair, try Sebastian Professional Trilliance Conditioner; for thick, L'Oreal Paris EverCreme Sulfate-Free Moisture System Deep Nourishing Masque.

Shopping: L'Oreal Paris EverCreme Sulfate-Free Moisture System Deep Nourishing Masque

The saboteur: Soggy styling. "Steam coming off your head is never a good sign," says hairstylist Jen Atkin. In fact, using hot styling tools on wet hair doesn't just damage strands—it scorches them. "Water boils at 212 degrees Fahrenheit," says Lewellyn. "The heat from a blow-dryer is around 250 degrees, and a flatiron produces a temperature nearly twice that amount." The sizzle you hear when you clamp down on wet—or even towel-dried—hair is actually the water inside the shaft bubbling and expanding. "Under a microscope, you can see the bulges and holes where the water evacuated."

The savior: Hair armor. Lightly mist on a heat-protecting spray, such as Nexxus Pro-Mend Heat Protexx Heat Protection Styling Spray, rather than a lotion, which is heavier and takes longer to dry. Blow-dry hair when it's damp, not wet, and wait for it to be 100 percent dry before flatironing, says Lewellyn.

Shopping: Nexxus Pro-Mend Heat Protexx Heat Protection Styling Spray

The saboteur: Sun exposure. "There's nothing like sun to leave your hair sad, drab, and brassy," says White. In fact, 100 hours of direct sunlight inflicts the same amount of damage as keeping bleach on your hair for 30 minutes, says Lewellyn.

The savior: SPF. Wear a hat or spritz on a UV filter before heading outdoors. "Leave-in products that contain benzophenone-3 or -4, butyl methoxydibenzoylmethane, polyquaternium-59, or cinnamidopropyltrimonium chloride are effective in protecting hair," says cosmetic chemist Ni'Kita Wilson. We like Kerastase Soleil Huile Céleste.

The saboteur: Shine-spray OD. The molecules inside silicone and argan oil—two common shine boosters—are unlikely to penetrate hair and can sit on top of it instead. "Eventually, those molecules form thin, water-repellent layers," says Andre Puleo, a senior project scientist at Unilever. In other words, they're like a rain jacket—deflecting the moisture that causes frizz, but also every other source of hydration. "Too much of the stuff can totally dry out your hair," says Dove celebrity stylist Mark Townsend.

The savior: Portion control. "I don't care how long or thick your hair is, a dime-size amount of serum is all it takes to bolster shine," says Townsend, who recommends almond and coconut oils as nondrying alternatives to argan oil. Those with fine hair should use a lightweight leave-in conditioner, such as Pantene Pro-V Aqua Light Weightless Conditioning Shake, instead of a glossing product, to boost shine without dragging hair down.

The saboteur: Tepid tools.
Lowering the temperature on your iron may seem like a prudent -- even praiseworthy -- move. In truth, it's not such a hot idea. "Low settings won't get the job done in one pass," says hairstylist Robert Vasquez of the Garren New York salon. "Ironing the same piece over and over is murder on hair."

The savior: Higher heat.
"The key is to find the right temperature for your hair type," says Lewellyn. A 425-degree setting will straighten thick, coarse strands -- and singe fine ones, which only need 300 to 325 degrees. "Play with a few settings to figure out which is the lowest one you can get away with," says Lewellyn.