1. Cranking up the heat-all the way: "You don't need 450 degrees," says hairstylist Nathaniel Hawkins; "410 works for every hair type.
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2. Forgetting protection: "Not enough people use thermal protectors," says hairstylist Matt Fugate. Look for a no-hold formula, like Suave Professionals Heat Protection Spray or Tresemme Heat Tamer Protective Spray.
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3. Running over (and over and over): Get hair as straight as possible before ironing by stretching out each section with a brush. Then slide the iron slowly and steadily in a single pass. "Don't stop and go, or you'll get horizontal lines," says hairstylist Garren.
4. Going board-straight: Instead of ironing hair straight, parallel to your face, move your arm in a C shape as you proceed down the hair, and bend the ends under.
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5. Ironing damp hair: If you hear a sizzling sound or see steam, well...it ain't good.
6. Thinking bigger is better: Hulking irons "make it harder to get to the hairline, where hair tends to be curliest," says hairstylist Sebastian Scolarici. Instead, choose a straightener with ceramic or tourmaline plates that are an inch wide.